StemBlock AI - Monthly Operational Cost Analysis
Date: February 27, 2026
Purpose: Comprehensive monthly cost breakdown including labor, infrastructure, and AI/token usage
Audience: Finance, Operations, Leadership
Executive Summary (Optimized with Vertex AI)
| Cost Category | Monthly Cost | Annual Cost |
|---|
| Employee Labor | $720 | $8,640 |
| Infrastructure (Neon + Hosting) | $27 | $324 |
| AI/Token Usage (Vertex AI Gemini) | $148 | $1,776 |
| TOTAL | $895 | $10,740 |
Target Budget: $1,000/month ✅ ACHIEVED
Infrastructure Update (Feb 2026): Migrating from DigitalOcean Managed PostgreSQL to Neon Serverless Postgres with native pgvector support. This enables the RAG pipeline to store vector embeddings directly in PostgreSQL (via document_embeddings table with HNSW indexing, 768D vectors using gemini-embedding-001), eliminating the need for a separate vector database service. At current scale (1 customer), Neon Free plan ($0/mo) covers our database needs. Infrastructure costs remain equivalent.
Optimization Summary
| Metric | Before (Mistral + DO) | After (Vertex AI + Neon) | Savings |
|---|
| AI Cost/Month | $6,479 | $148 | 97.7% |
| Infrastructure/Month | $27 | $17 | 37.0% |
| Total Cost/Month | $7,226 | $885 | 87.8% |
| Annual Cost | $86,712 | $10,620 | $76,092 |
1. Employee Costs
Current Staffing
| Role | Hours/Month | Hourly Rate | Monthly Cost |
|---|
| Employee | 40 | $18.00 | $720 |
Annual Employee Cost: $720 × 12 = $8,640
Cost Breakdown by Activity (Estimated)
| Activity | Hours/Month | % of Time | Cost |
|---|
| Development & Maintenance | 16 | 40% | $288 |
| Testing & QA | 8 | 20% | $144 |
| Support & Bug Fixes | 8 | 20% | $144 |
| Documentation & Planning | 4 | 10% | $72 |
| Meetings & Communication | 4 | 10% | $72 |
| TOTAL | 40 | 100% | $720 |
2. Infrastructure Costs (Neon + Hosting)
Current Monthly Spend
| Resource | Specification | Monthly Cost |
|---|
| App Platform / Hosting | Basic tier | ~$12 |
| Database (Neon Serverless Postgres) | Free plan (100 CU-hours, 0.5GB) | $0 |
| Database (Neon Launch plan, when needed) | Pay-as-you-go ($0.106/CU-hour) | ~$15 |
| Storage / CDN | As needed | ~$5 |
| TOTAL (current, Free plan) | | ~$17 |
| TOTAL (projected, Launch plan) | | ~$32 |
Annual Infrastructure Cost (current): $17 × 12 = $204
Annual Infrastructure Cost (Launch plan): $32 × 12 = $384
Why Neon Over DigitalOcean?
| Factor | DigitalOcean Managed DB | Neon Serverless Postgres |
|---|
| pgvector support | Not included | Native extension, no extra cost |
| Scaling | Fixed instance size | Autoscale 0.25–16 CU, scale-to-zero |
| RAG vector storage | Requires separate vector DB | Built-in via pgvector |
| Cost at idle | ~$10/mo (always running) | $0 (scales to zero after 5 min) |
| Cost at scale | $60+/mo (Professional tier) | $0.106–0.222/CU-hour (pay for usage) |
| Connection pooling | Not included | Built-in PgBouncer |
Neon Plan Scaling Path
| Stage | Neon Plan | Est. Monthly | Triggers |
|---|
| Current (1 customer) | Free | $0 | 100 CU-hours, 0.5GB sufficient |
| Growth (5–30 customers) | Launch | $15–50 | Exceed free tier compute/storage |
| Scale (50–300 customers) | Scale | $69–300 | Need >16 CU, private networking, SLAs |
3. AI/Token Usage Costs (Optimized with Vertex AI)
Provider Configuration
| Feature | Model | Reason |
|---|
| English Writing | Gemini 2.5 Pro | Higher quality for nuanced writing feedback |
| STEM Evaluation | Gemini 2.5 Flash | Fast, cost-effective for structured evaluation |
| Coach Feedback | Gemini 2.5 Flash | Fast, cost-effective |
| Parent Insights | Gemini 2.5 Flash | Fast, cost-effective |
Vertex AI Gemini Pricing (Per 1M Tokens)
| Model | Input (≤200K) | Output | Cached Input |
|---|
| Gemini 2.5 Pro | $1.25 | $10.00 | $0.125 |
| Gemini 2.5 Flash | $0.30 | $2.50 | $0.030 |
Optimized AI Costs (With Caching Implemented)
STEM Evaluation (Gemini 2.5 Flash)
- Volume: 4,800 submissions/month
- Caching: 50% hit rate (7-day cache) → 2,400 actual API calls
- Tokens/call: ~3,000 input + ~600 output
| Component | Monthly Tokens | Rate | Cost |
|---|
| Input | 7.2M | $0.30/M | $2.16 |
| Output | 1.44M | $2.50/M | $3.60 |
| Subtotal | 8.64M | | $5.76 |
Cost per evaluation: $0.0024 (vs $0.67 before)
English Writing Workflow (Gemini 2.5 Pro)
- Volume: 1,900 submissions/month
- 3-stage pipeline: Moderation → Feedback → Assessment
- Tokens/submission: ~2,500 input + ~3,500 output
| Stage | Tokens (Input/Output) | Cost |
|---|
| Moderation | 1.0M / 0.5M | $1.25 + $5.00 |
| Feedback | 1.5M / 1.5M | $1.88 + $15.00 |
| Assessment | 2.0M / 1.5M | $2.50 + $15.00 |
| Subtotal | 4.5M / 3.5M | $40.63 |
Cost per submission: $0.021 (vs $0.88 before)
Coach Feedback Generation (Gemini 2.5 Flash)
- Volume: 1,920 calls/month
- Caching: 30% hit rate → 1,344 actual API calls
- Tokens/call: ~3,000 input + ~700 output
| Component | Monthly Tokens | Rate | Cost |
|---|
| Input | 4.0M | $0.30/M | $1.20 |
| Output | 0.94M | $2.50/M | $2.35 |
| Subtotal | 4.94M | | $3.55 |
Cost per feedback: $0.0026 (vs $0.71 before)
Parent Insights (Gemini 2.5 Flash)
- Volume: 1,500 generations/month
- Caching: 85% hit rate (1-week cache) → 225 actual API calls
- Tokens/call: ~1,500 input + ~500 output
| Component | Monthly Tokens | Rate | Cost |
|---|
| Input | 0.34M | $0.30/M | $0.10 |
| Output | 0.11M | $2.50/M | $0.28 |
| Subtotal | 0.45M | | $0.38 |
Cost per insight: $0.0017 (vs $0.14 before)
AI Cost Summary (Optimized)
| Feature | Volume/Month | Actual Calls | Monthly Cost | Cost/Use |
|---|
| STEM Evaluation | 4,800 | 2,400 | $5.76 | $0.0024 |
| English Writing | 1,900 | 1,900 | $40.63 | $0.021 |
| Coach Feedback | 1,920 | 1,344 | $3.55 | $0.0026 |
| Parent Insights | 1,500 | 225 | $0.38 | $0.0017 |
| Subtotal | | | $50.32 | |
| Vertex AI Platform Fee (~10%) | | | $5.03 | |
| Buffer/Overhead (~50%) | | | $25.16 | |
| Network Egress (est.) | | | $10.00 | |
| TOTAL AI COST | | | $90.51 | |
Conservative Estimate (with 50% buffer): ~$148/month
Annual AI Cost: $148 × 12 = $1,776
4. Before vs After Comparison
Cost Reduction by Feature
| Feature | Before (Mistral) | After (Vertex AI) | Reduction |
|---|
| STEM Evaluation | $3,226 | $5.76 | 99.8% |
| English Writing | $1,673 | $40.63 | 97.6% |
| Coach Feedback | $1,370 | $3.55 | 99.7% |
| Parent Insights | $210 | $0.38 | 99.8% |
| TOTAL | $6,479 | $50.32 | 99.2% |
Cost Per Use Comparison
| Feature | Before | After | Savings |
|---|
| STEM Evaluation | $0.67 | $0.0024 | 99.6% |
| English Writing | $0.88 | $0.021 | 97.6% |
| Coach Feedback | $0.71 | $0.0026 | 99.6% |
| Parent Insights | $0.14 | $0.0017 | 98.8% |
5. Total Monthly Cost Breakdown (Optimized)
Summary
| Category | Monthly Cost | % of Total | Annual |
|---|
| Employee Labor | $720 | 81.4% | $8,640 |
| AI/Token Usage | $148 | 16.7% | $1,776 |
| Infrastructure (Neon Free + Hosting) | $17 | 1.9% | $204 |
| TOTAL | $885 | 100% | $10,620 |
Visual Breakdown
Total: $885/month (Target: $1,000) ✅ Under Budget
┌─────────────────────────────────────────────────────┐
│ Employee Labor (81.4%) │████████░ $720 │
├─────────────────────────────────────────────────────┤
│ AI/Token Usage (16.7%) │██ $148 │
├─────────────────────────────────────────────────────┤
│ Infrastructure (1.9%) │ $17 │
└─────────────────────────────────────────────────────┘
Budget Remaining: $115/month (11.5% headroom)
6. Scaling Analysis
Room to Grow Within $1,000 Budget
With $115/month headroom, you can increase usage:
| Scenario | Additional Capacity | New AI Cost | Total Cost |
|---|
| +50% STEM Evaluations | +2,400/month | +$3 | $888 |
| +100% English Writing | +1,900/month | +$41 | $926 |
| +100% All Features | 2x volume | +$50 | $935 |
| Maximum Scale (Free plan) | 3x current | +$100 | $985 |
| With Neon Launch plan | 5x+ current | +$100 | $1,000 |
Cost at Different Usage Levels
| Usage Level | AI Calls/Month | AI Cost | Total Cost | Status |
|---|
| Current | 10,120 | $148 | $895 | ✅ Under Budget |
| 2x Current | 20,240 | $246 | $993 | ✅ At Budget |
| 3x Current | 30,360 | $344 | $1,091 | ⚠️ Over Budget |
| 5x Current | 50,600 | $540 | $1,287 | ❌ Over Budget |
7. Implementation Checklist
Completed ✅
Required for Neon Migration
Required for Vertex AI Migration
Vertex AI Setup Costs (One-Time)
| Item | Cost |
|---|
| GCP Project Setup | Free |
| Vertex AI API Enable | Free |
| Initial Testing (~1M tokens) | ~$3 |
| Total Setup Cost | ~$3 |
8. Cost Per User Metrics (Optimized)
Assumptions
- 500 active coaches
- 2,000 active students
- 500 active parents
Cost Per User (Optimized)
| User Type | Count | Monthly Cost | Cost/User |
|---|
| Coach | 500 | $895 | $1.79 |
| Student | 2,000 | $895 | $0.45 |
| Parent | 500 | $895 | $1.79 |
| Per Active User (All) | 3,000 | $895 | $0.30 |
Comparison
| Metric | Before | After | Improvement |
|---|
| Cost per user | $2.41 | $0.30 | 87.6% lower |
| Cost per coach | $14.45 | $1.79 | 87.6% lower |
9. Revenue vs. Cost Analysis (Optimized)
Current Subscription Revenue
| Tier | Users | Price | Monthly Revenue |
|---|
| COMMUNITY | 450 | $0 | $0 |
| TEAM | 40 | $29 | $1,160 |
| ENTERPRISE | 10 | $299 | $2,990 |
| TOTAL | 500 | | $4,150 |
Profitability Analysis (Optimized)
| Metric | Before | After |
|---|
| Monthly Revenue | $4,150 | $4,150 |
| Monthly Costs | $7,226 | $895 |
| Monthly Profit/Loss | -$3,076 | +$3,255 |
| Annual Profit/Loss | -$36,912 | +$39,060 |
Status: ✅ NOW PROFITABLE
Gross Margin
| Metric | Value |
|---|
| Revenue | $4,150 |
| Costs | $895 |
| Gross Profit | $3,255 |
| Gross Margin | 78.4% |
10. Key Metrics Dashboard (Optimized)
Monthly KPIs
| Metric | Target | Optimized | Status |
|---|
| Total Monthly Cost | <$1,000 | $895 | ✅ On Target |
| AI Cost per Evaluation | <$0.10 | $0.0024 | ✅ Excellent |
| Cost per Active User | <$1.00 | $0.30 | ✅ Excellent |
| Employee % of Total | <85% | 80.4% | ✅ On Target |
| Revenue : Cost Ratio | >1.0 | 4.64 | ✅ Excellent |
| Gross Margin | >50% | 78.4% | ✅ Excellent |
Budget Utilization
Monthly Budget: $1,000
Spent: $895 ████████████████████░░░ 89.5%
Remaining: $105 ░░░░░░░░░░░░░░░░░░░░░░░ 10.5%
11. Risk Factors & Mitigations
Potential Cost Increases
| Risk | Impact | Mitigation |
|---|
| Token price increase | +$50-100/month | Lock in pricing, monitor alternatives |
| Usage spike (viral growth) | +$50-150/month | Implement rate limiting, tier quotas |
| Model deprecation | Migration effort | Stay on stable/GA models |
| Vertex AI outage | Service disruption | Maintain Mistral fallback |
| Neon cold start latency | 500ms–2s on first query | Health check ping every 4 min in production |
| Neon Free plan limits exceeded | Need to upgrade to Launch ($15/mo) | Monitor CU-hours via Neon Console |
Cost Monitoring
- Set up GCP billing alerts at $75, $100, $150
- Weekly token usage review
- Monthly cost reconciliation
12. Summary
Monthly Cost Achievement
| Component | Cost | Target | Status |
|---|
| Employee | $720 | - | Fixed |
| Infrastructure (Neon Free + Hosting) | $17 | - | Variable |
| AI (Vertex AI) | $148 | - | Variable |
| TOTAL | $885 | $1,000 | ✅ 11.5% Under |
Annual Savings
| Metric | Amount |
|---|
| Previous Annual Cost | $86,712 |
| Optimized Annual Cost | $10,620 |
| Annual Savings | $76,092 |
Key Optimizations Applied
- ✅ Caching implemented - 50-85% reduction in API calls
- ✅ Switched to Vertex AI Gemini - 97-99% reduction in token costs
- ✅ Model tiering - Gemini 2.5 Pro for quality, Flash for speed
- ✅ Neon + pgvector migration - Serverless PostgreSQL with built-in vector DB, scale-to-zero, ~$10/mo savings vs. DigitalOcean
Appendix: Vertex AI Pricing Reference
Gemini 2.5 Pro (Per 1M Tokens)
| Type | ≤200K Context | >200K Context | Cached |
|---|
| Input | $1.25 | $2.50 | $0.125 |
| Output | $10.00 | $15.00 | N/A |
Gemini 2.5 Flash (Per 1M Tokens)
| Type | ≤200K Context | >200K Context | Cached |
|---|
| Input | $0.30 | $0.30 | $0.030 |
| Output | $2.50 | $2.50 | N/A |
Source: Vertex AI Pricing
Document Version: 3.0
Last Updated: February 27, 2026
Status: Active - Neon + pgvector Migration
Owner: Operations Team
Next Review: March 27, 2026