[onion2k]

My understanding is that this is a difficult problem to solve "perfectly" due to lag between incurring a cost and recording the cost.

It's impossible to solve perfectly with tech.

Amazon saying "If you put a number in this form we won't charge you more than that, but your account will be limited by <list of limitations> and if you go over those limits then <long list of conditions that will apply if you go over the limits up to and including removing you from the platform if AWS think it was fraudulent>" is a perfect solution.

The only reason why there would need to be a perfect tech solution is if AWS are concerned about giving people a small amount of service that they're not able to charge for. AWS clearly believe protecting themselves from overages is more important than giving customers peace of mind that they're not going to be hit with a huge bill. That's a reasonable position for a business to take, and they're completely free to do it, but you can't also argue that customers are wrong to avoid deploying to AWS because they're scared of a surprise bill.