People like Windsurf and Cursor because they offer them a flatrate.
So I tend to start with Devstral unless I know it will struggle, and then move on to paid models as needed. When I do switch to a paid provider, it's noticeably better than the same provider on a Cursor paid plan, so even though it's more expensive, I feel like there's more value there.
I honestly don't have a proper monthly tally yet. I've used $30 in OpenRouter credits over a couple weeks, but a lot of that was experimenting to compare quality of output.