Both the SSR-85 B's & C's originally retailed for about $580, and I have seen some in the last couple of months selling in the $500 range. I would not pay over $600 like many are asking.
I think $450 to $525 is a good price. They can be found at this price.
I do not own a SSR-85(wish I did), but these are the differances that I do know.
The SSR-85B is an AKM version with a thinner(lighter) barrel.
The SSR-85C is the AK-47 version with heavier barrel, vented gas tube, and larger front sight.
These rifles were originally built on the FEG receivers, but Global did manufacture some on the OOW receivers this last year. I would first make sure the SSR-85C is built on the FEG receiver.
I am sure others can add much more information than I did, but that as much as I know about these rifles.
Good luck!