I think the solution is some sort of PoW gateway like people are setting up now. Or a micropayments system where each page request costs a fraction of a penny.

You could combine that with some sort of IPFS/Bittorrent like system where you allow others to rehost your static content, indexed by the merkle hash of the content. That would allow users to donate bandwidth.

I really don't like the idea that you can get out of this by surveiling user agents more or distinguishing between "good" and "bad" bots which is a massive social problem.