A National Semiconductor IMP-16C recently appeared on eBay. The IMP-16C was an early 16-bit microcomputer and was produced in small numbers (the item description says 100 were made, which is probably accurate). The seller also claims it might be the only one, but I doubt that. It might be the best surviving example, however, as it is working and in good cosmetic condition.
The final sale price was $5,500, an impressive price considering there aren’t legions of National Semi collectors out there.