"How much will the API cost?" Real answer: API is only 40-50% of the total.

Monthly breakdown (real SaaS)

LLM tokens ~$20k, embeddings ~$80, vector DB $350, app infra $810, monitoring $630, human time $2k, hidden costs $700. Total ~$24k/month for 2500 MAU.

Levers

Prompt caching, smart routing, batch API, per-user caps.