I'll see myself out of this discussion. I can get Ms for $2 a piece.
I hunt around for model M bargains all the time. Right now the best looking one is a lexmark for $11 + $17 shipping that's missing keycaps and possibly the cable. Finding a model M in any condition under $40 shipped is a good deal, and one with all the keycaps and cable is an excellent deal.
The cheapest I have ever paid for a model M is this 1390120 I got with no cable and only some keycaps for $15 + $12 shipping, which is an absolute steal IMO as it was in excellent condition and included a mandolin crystal (and barcode label)
I will buy any model M in any condition for $10.
Now, is $100 too high for a model M in an uncommon-but-not-actually-rare case? Probably not, but $60 for a decent M in good shape isn't too bad and I would probably pay an extra $10 or $15 over my usual price for something that's got an uncommon feature. Solid keycaps are extra $5 at least in my book.
Now, having said that: no-one outbid me on the 3 Ms I have my hooks into right now. They're gonna be restored and resold on GH at cost.