The person above was talking about the cost of HDDs, they didn't include the cost of a machine or NAS to run them in so why should I?

Seems like a double standard wherein people are going to pretend housing multiple HDDs costs $0 (unrealistic) but won't even evaluate spending money on a tape drive.

You what doesn't get cryptolockered? Yesterday's tape sitting on the shelf.

Because we're talking about most people, and most people already have a machine into which they can plug a HDD. Often that's the very machine with the documents they want to backup.

I think "plugs into SATA or USB" is a reasonable standard for a backup storage medium.

Whereas I think that isn't a backup at all, because it is plugged into the same machine (i.e. online backup) and therefore going to get crypto-lockered.

A USB drive hooked up via ESATA or USB is directly comparable to an LTO tape.

So is a tape left in the drive.

If you can move a tape to a shelf, you can unplug a USB cable.

And to your question about having a separate machine, a Pi will be fine.

Neither SATA nor USB implies permanence.