Tarsnap seems very expensive.

I'm backing up about 8TiB of data nightly using BorgBackup[0] + InterServer[1] and pay $240/yr.

This gives me differential encrypted rotating backups that are 100% mine and do not lock me into any specific storage vendor.

[0] https://borgbackup.readthedocs.io/en/stable/

[1] https://www.interserver.net/storage/