[throw0101b]

> The last time I looked it could easily cost hundreds of dollars per month to back up as little as 40TB to the cloud.

You only have to backup the data that is important to you and you don't want to lose in case your house gets robbed, floods, burns down, etc.

If you don't mind losing 40T of data, you don't have to back it up at all.

Otherwise get another NAS, installed it at family/friend's house, and set up a VPN between the two: then use rsync/zfs-send/whatever.