Disclaimer: I wrote this article and made this website.
There was some talk of this issue in the recent fediverse inefficiencies thread. I’m hopeful that in the future we’ll have a decentralized solution for file hosting but for now I deeply believe that users should pay for their own file hosting.
Fedi software like Misskey already did exactly that. Each user have limited “drive” which can be upgraded/customized per user. People even reuse image they already have on their drive, so it won’t be any duplicate files.