P5/P6: why so cheap???

[ZombieLaMuerta]

I've been watching eBay and various classifieds with some interest recently and the one thing that seems to grab my attention is that the P5 and P6 seem to be very reasonably priced for a car of its vintage, the engine is a benefit.

What I want to know is why?

It could be a potential purchase at some point, but is there something buyers should be made aware of?