This really underscores Amazon's glaring omission of a billing cutoff on Amazon web services. How hard would it be for them to let me say, cut off my services at $100/month? This is the main reason I'd never use AWS to host anything public.
I guess that would be a nice feature to offer as an option, but most people would not want their web service cut off if they get a spike in traffic.
Those of us who can't afford an extra £1000/month (or more if it's a dedicated attack) would love to be able to just turn it off when a threshold is hit.
Users may lose access, but at least you don't go bankrupt in the process.