i've been using restic daily to a local store (with compression and encryption turned on), and then once restic has finished its daily run then i rclone to backblaze. i keep one snapshot per day for a week, 1 weekly snapshot for a month, and 6 monthly snapshots. i pay about £1 per month for about 250GB of data (prior to compression / encryption).
for those unfamiliar to restic, you can mount a r/o snapshot via fuse for ease of access as well as the command line tool to programmatically access the repo.
Why don't you let restic upload directly to backblaze? I am sure you know this is possible, just wondering on why you made that choice, not trying to be a smartass ;).
I did at first but the latency was a killer; it took about 2~3 hours to make a snapshot. If I did the snapshot locally and then used rclone to back up the restic repo to BB then the whole operation took about 15~20 minutes, and the snapshot itself took less than 5; if the rclone gets interrupted you can just restart it.
for those unfamiliar to restic, you can mount a r/o snapshot via fuse for ease of access as well as the command line tool to programmatically access the repo.