Every prompt costs money. Every debug session. Every "fix this error" request. Every audit sweep.
Flagship AI models charge $2–5 per million input tokens and $4–30 per million output tokens. Sounds tiny until you're running four parallel research agents to audit a codebase, each consuming thousands of tokens per analysis. A single comprehensive QA sweep can burn $20–$50 in API costs alone. And if you're doing it right, you're doing it before every launch — not once, but iteratively.
And your developer isn't just "using AI." They're orchestrating a database with Row Level Security policies, authentication flows with email confirmation, payment webhooks with idempotency guards, file storage with proper permissions, edge functions for server-side logic, and migration tracking so environments don't drift.