Backblaze is $6/TB so should be cost effective for this amount of data.

I think all the recommended backup SW (restic, duplicity) encrypt before storing. I use restic but haven't exactly been hugely exercising it, so can't place much weight on my experience . But it should be okay with this quantity of data.

Generally I'd guess that diversity of backups wins over using a single expensive one in terms of reliability, but at the expense of more overhead managing them.