In 2020 you needed $5k/mo just to run a basic SaaS. In 2026, free tiers have caught up — and a 200-user AI product can run at literally $0/month if you pick the right stack. Voxly is doing it at 240 testers right now. Here's the exact playbook plus the revenue thresholds where you actually need to start paying.
The $0 stack (every layer)
| Layer | Service | Free tier limit |
|---|---|---|
| Hosting / SSR | Vercel Hobby | 100GB bandwidth/mo, unlimited deploys |
| Database | Supabase Free | 500MB DB, 1GB file storage, 50k auth users |
| Auth | Supabase Auth (free) | 50k MAU; email + Google + Apple included |
| AI inference | Anthropic free tier OR BYO keys | $5 starter credit + free OAuth keys from users |
| Voice/audio | Groq (Whisper Free) | Very generous free quota, ~10× faster than OpenAI |
| Resend free | 3,000 emails/mo | |
| Edge / CDN | Cloudflare | Unlimited bandwidth, free SSL, free Workers (100k req/day) |
| Analytics | Plausible (self-host) OR GA4 | Self-hosted = $0; GA4 always free |
| Error tracking | Sentry Developer | 5k events/mo |
| Domain | Cloudflare Registrar | At-cost (~$10/yr) — the only real cash you spend |
Total fixed monthly cost: $0. Domain is ~$1/mo amortized.
The BYO-keys trick
Voxly's clever move: let users plug in their own Anthropic / OpenAI / Gemini API keys. Each user pays for their own inference. Your AI inference cost drops to $0 forever.
Two upsides nobody talks about:
- Privacy moat. "Your audio never touches our servers" is a real selling point for enterprise.
- Customer lock-in via configuration, not vendor. Once they've set up their keys + glossary + tone profile, they're sticky.
The downside: friction for non-technical users. Solution: tiered model. Free tier = BYO keys required. Paid tier = we cover inference up to limits.
Real cost breakdown: Voxly at 240 users
Here's Voxly's actual monthly bill at 240 active testers, ~3 recordings/user/week, average 30 seconds each:
- Vercel Hobby: $0 (well within bandwidth)
- Supabase Free: $0 (DB is 47MB; auth is 240 users)
- Anthropic (BYO keys + free credits): $0 for Voxly
- Groq Whisper (free tier): $0 — ~9,000 recordings/mo well within limits
- Resend: $0 (~1,200 emails/mo for magic links)
- Cloudflare: $0
- Plausible (self-hosted on a $5 DigitalOcean droplet): $5
- Domain (yearly amortized): $0.83
- Sentry (free tier): $0
Total: ~$6/month for 240 active users. ARPU at $0 since we're in beta, but the unit economics are obviously crazy in our favor.
When to upgrade (the thresholds)
- Hit 100GB bandwidth/mo → upgrade Vercel. Typically happens around 5k–10k active users. Pro tier starts at $20/mo.
- Hit 500MB database → upgrade Supabase. Usually around 2k–5k power users. Pro tier is $25/mo and includes daily backups (worth it before you have paying customers).
- Hit 5k Sentry events → upgrade. Happens fast if you have any UI bugs. Team tier is $26/mo.
- Need SLA + uptime monitoring → upgrade everything. Once you have $X enterprise contracts, expect to spend $200–$500/mo across the stack.
What NOT to put on the bootstrap stack
- AWS / GCP from day 1. You don't need EC2, RDS, EKS, ALB. They're cheaper at scale but more expensive at zero scale (operationally and cognitively).
- MongoDB Atlas. 500MB free is real but Postgres + Supabase outperforms for AI workloads (vector ext, RLS, JSON columns).
- Auth0 / Clerk Pro. Free tiers are fine for < 5k users but Supabase Auth ships with the same DB so there's no integration tax.
- Datadog / NewRelic. Overkill before you have revenue. Use Sentry + Plausible + your dashboard.