I’m not sure if R2 is sustainable but AWS’s egress rates are outrageous. The flip side though is that high egress rates make quite a few problems, like customers using the service to distribute pirate copies of media, go away.
Backblaze, an online storage and backup company, is also a member. They charge $.005/GB/month for S3 compatible storage. And if you map and access a bucket through Cloudflare there is no egress fee.
So it's possible to store and access your files at 1/3 the price of Cloudflare alone by using Cloudflare (plus Backblaze).