The guy clearly is working on what I generally describe as the Amazon Marketplace out-of-print bookseller model: mark it up as high as possible, and hope some sucker bites.
I mean, if I could sell a
PA 50mm f2 for the price he's asking for I'd head on down to the local camera shop and buy up their entire stock, even with their usual lens markup.
(On the other hand, I'm not certain what's more insulting about his
Mount Adapter K listing: the incredibly optimistic pricing, or the fact that he's charging $42 international shipping for a tiny ring of metal.)