They really are quite rare. But this auction was asking too much. 500$-1k$ would be too much for me, but for a complete setup a more reasonable price to ask. Consider that once the user hosed their Genera partition that they would have no way to restore it, this would be an expensive gamble. I saw a MacIvory 3 system years ago go for about $500 and I balked that I'd surely find one cheaper... hasn't happened yet! Just my luck that I never have the money when a cool, rare dreamgadget becomes available.
The fastest Symbolic setup ever was OpenGenera, the system ported to a virtual machine run on DEC Alphas under Tru64 UNIX (aka Digital UNIX, aka OSF/1). And if you poke around, you may find that a few people have been quietly tweaking OpenGenera to run on modern 64-bit systems, such as Linux and MacOS. Personally, I am going to wait until I fix my Alpha to bother with it.