Earlier quoted context omitted.
Which clouds do this? I work quite a bit with AWS and GCP, and Azure to a lesser extent, and I've yet to see a spending limit on any of them. I'd love to be proven wrong though.
GCP definitely has a spending limit. Of course it also (at least in the past) used to take 24 hours to update, so if you had a massive spike in real usage, your site would die for a day while you frantically tried to increase the limit.
The best you can do is build your own service to monitor your bill and manually cut off your billing account if it gets too high. Hope you did it correctly because there's no good way to test it! And the bill notifications can be delayed an arbitrary amount of time with no guarantees, and disabling billing can take an arbitrary amount of time too, so you can still be screwed even if you did it correctly.
I think it's a glaring hole in cloud platforms. I get it, it's hard to implement in a way that is forgiving and doesn't cause a bunch of support tickets from people who set their limits too low and made their site go down. But that's why people use cloud platforms, so they don't have to implement the hard part. It's beyond me why the cloud platforms don't do something better here.