As long as these companies have an API, I imagine it's going to be cheaper to pay a la carte than pay monthly. $250 is a lot of API calls, especially as competition drives the cost lower. For stuff not behind an API, you're kinda shooting yourself in the foot because other providers might and at the very least it means developers aren't going to adopt it).
It might not be as many API calls as you think. Taking OpenAI as an example, if you're using the most expensive models like o3, gpt-4.5, o1-pro, etc. heavily for coding in large codebases with lots of context, you can easily spend hundreds per month, or even thousands.
So for now, the pro plans are a good deal if you're using one provider heavily, in that you can theoretically get like a 90% discount on inference if you use it enough. They are essentially offering an uncapped amount of inference.
That said, these companies have every incentive to gradually reduce the relative value offered by these plans over time to make them profitable, and they have many levers they can use to accomplish that. So in the long run, API costs and 'pro plan' costs will likely start to converge.
