is there an way to figure out what would different options cost if you rely on vapi instead of adding your own api keys. Like estimated per min cost for STT, LLM, TTS in the available options so its easy to compare?

Vapi will not cost differently. It will be same if u use your own key or the same provider via Vapi. We will only charge you a fixed 0.05$ per minute. The rest cost will be by the corresponding provider.