Earlier quoted context omitted.
I've dealt with this before. The problem with doing a billing cap is that now you are bringing an out-of-band batch system (billing) in-band. The only way to do a dollar cap is to constantly calculate your bill. Capping it at 100K requests is a lot easier, because it's a single number that can be incremented easily in a distributed way. It's the same reason it took AWS forever to offer billing caps, and even today, t…
How about implementing a prepaid system where you set your budget, and if you exceed it, everything just pauses until you pay more?
It is a very solvable problem, I just don't think pre- vs postpaid changes it.