[Enhancement]: Estimate token usage cost

### Before Requesting

- [X] I have searched the existing issues, and there is no existing issue for my feature request

### What feature do you want?

I use [Niek/chatgpt-web](https://github.com/Niek/chatgpt-web) that has a neat feature to estimate cost per request and total cost.

https://github.com/search?q=repo%3ANiek%2Fchatgpt-web+tokens&type=code

Would love to see something similar in CPX.