I've seen them offered (with some interest) at $485 retail. This is for a MAK-90 with the underfolder trunnion and threaded barrel in perfect condition.
Here's the deal, though. At present, the gun can not be converted into an assault rifle so I fail to see the added value over any other MAK-90. Even if the AWB sunsets, that does not necessarily mean the gun would magically become convertible.
The autonomic nervous system provides for involuntary muscle function - the work of breathing, digestion, and so forth. On some folks, that's a pure waste of ingenuity.