When servers got slashdotted it was almost, even way back then, running out of CPU/Database connections, not bandwidth.
a) you're a hobbyist/minor (effective budget of $0)
b) you're on cloud hosting and go over without a budget set
Like I said above, I did all the stuff I did with nothing more than $5/$10 month cloud hosting plans. Almost no one is going to hit any kind of bandwidth limits these days unless they are trying to run SaaS or just pirating full BluRays in the dumbest ways possible. But we're not talking about those people, we're talking about hobbyist content creators.
That being said, I do pay for a monthly plan, because relying on free handouts for anything that matters is never a reasonable approach.
Simply being sensible about what kind of files you're asking people to download solves 99.9% of this problem and makes your site more enjoyable (faster) for users (especially mobile ones).
A $5/mo digital ocean instance comes with 1TB of transfer. That's a lot unless you're doing something like self-hosting video.
Heroku free tier includes up to 2TB/month.
Even the free tier of AWS comes with 15GB/month.
But all that aside, this product exists already, it's called a CDN.