The price is high but not all that bad, and only once before have I ever seen a new one turn up. 3 available...
Yes, that's a reasonable price for what looks like an unused F-122... And gosh, how often do they turn up? I don't think I've
ever seen one, actually.
Interesting. It doesn't specify in the auction, but do you think these would just plug up to a PC or would they definitely need the converter?
These have a special 270-degree DIN connector (sort of like the large AT connector, but the pins are farther apart). You'd definitely need
something like this to use it with a PC. You could also replace its internal controller with a Teensy, which has the advantages of being cheaper (only about $12 I think) and invisible. There are lots of posts about that here.
The F122 looks like it's in great condition although it's missing the keycap-top to the bottom left of the numeric Enter-key...
That's trivial. Model M and F caps are interchangeable, and that particular one is just the standard " . Del" numpad key. You could use one from a Model M, or ask here on GH if anyone had an extra one they could spare.
Maybe they were used for a while and then stored away?
It says they've been stored "their entire lives", so I'd take that to mean there was no wear on them at all. It certainly looks that way from the photos.
It also looks like the label on one is peeled a bit on the bottom left corner...
Again, that looks easily fixable. Also, remember, there are three of these, so you could just ask for one of the others instead—with the understanding that it was otherwise in the same perfect condition.