I’d be surprised if you find cheaper, but if you do, please report back.

Fwiw, BB have been super reliable for me over that past few years I’ve used them.

There’s a plan where you pay some tiny amount per gb. Thats the one to use.

I use restic to backup immich (and everything else) to b3.

Be sure to stop the docker container while you backup to avoid skew.

Backblaze saved my ass at the end of last year when I had a hardware failure.

You could do a dry run with rsync and see what it reports needs update.

I think you’d have to force it to use checksums instead of time stamps.