For Google Cloud can't you set a billing limit for it to not exceed? That's what I have done but I have not come close to exceeeding it yet so IDK if there is something I am missing.
You can. Beware though! It can take 24 hours to increase the limit - horrible if you get a sudden spike in traffic from, say, a techcrunch post or something.
Should be fine I think providing there are no circumstances where Google can decide to ignore the limit (don't have much experience with their cloud stuff).
I think these billing limits only apply to AppEngine services.
Ahh I think you are right. Just checked and you can set limits for App engine, but there are budgets in Google Cloud which is confusing and doesn't seem like it actually limits anything, it just keeps you notified of how much you are spending relative to your budget