I wish AWS and other clouds would cater to this crowd (which I'm a part of). I just closed my AWS account to remove this exact risk. I love hacking around and playing with the various services—it satisfies my own curiosity and also helps me at work—but it's not worth putting my financial security at risk to keep these accounts open. More than once I've stress-checked my AWS bill in the middle of the night because I was worried there'd be some hidden bill or somebody hacked in and blew up the network traffic or compute or whatever. It's just not worth the loss of peace of mind.

I wonder if a potential solution is to have two billing modes that get hardlocked at signup (or require a key or something to change): one is the standard model with alerts etc. The other is a personal model that kills all of your stuff when you go over some limit. I would feel much safer if the latter were in place.