The majority of these massive bills are due to traffic, there is pretty much no way that AWS could stop your server in time...if they had the choice, which they don't.

I think my original point was unclear: I am pointing out that if you just think about how this stuff can possibly work, billing alerts can not work in the way you expect. The alert is updated async, the horse has bolted and you are trying to shut the gate.

I don't use AWS for personal stuff because I know their billing alerts won't stop me spending a lot. Don't use them if that is a concern.

I do use AWS at work, we are a relatively big customer and it is still very expensive for what it is. The actual hardware is wildly overpriced, their services aren't particularly scalable (for us), and you are basically paying all that overage for network...which isn't completely faultless either. Imo, using them in a personal capacity is a poor idea.