As the post says, the problem with coding agents is they send a lot of their own data + almost your entire code base for each request: that's what makes them expensive. But when used in a chat the costs are so low as to be insignificant.

I only use OpenRouter which gives access to almost all models.

Sonnet was my favorite until I tried Gemini 2.5 Pro, which is almost always better. It can be quite slow though. So for basic questions / syntax reminders I just use Gemini Flash: super fast, and good for simple tasks.