Anyone is welcome to join my instance at endlesstalk.org. Its running on a pretty beefy server, so it can take a decent amount of users.
There are multiple frontends like lemmy.world and I have setup a seeder(lemmony), so the all feed should be pretty filled.
For s3 iDrive e2 is cheaper. It costs 4$ per month, if you pay monthly and down to ca 3$, if you pay yearly.
The egress policy is mostly the same as backblaze. You get 3 times the storage you pay for. With backblaze you get 3 times the average amount of data you have stored.