You pay a different rate per model (OpenRouter shows the pricing transparently). You load your account with credits. I use it daily (undoubtedly far more than the average user) and loaded 50$ with credits five months ago, but I still have over 1/2 of it left.
I think it is hard to believe that Kagi would be any cheaper and have no rate limits.
At AirGradient, all our air quality monitors can completely run local. Our official firmware is on GitHub and people could even flash their own (adjusted) version.
We believe this is how IoT devices should be and are very vocal about it. So I think there are a few manufacturers that think different.