Cloudflare. You will get a call if on a free or pro ($25/month) plan [1] if your bandwidth usage is so high it would warrant increasing your plan. Worst case, they turn you off. Preferred over denial of money attack based on your use case. Set and forget after pointing at your origin (time is money).
You'll get a call on any of their plans if your bandwidth usage exceeds certain thresholds, I am assuming your median usage is relatively tame.
Disclosure: Cloudflare enterprise customer, no other affiliation. I don't get anything for saying nice things.