Just use logic and reason to determine the price. The first question that you need to ask yourself is what is a bayonet worth. After all, a pre-ban Norinco sells for upwards of $1100 dollars now. The difference between it and your model should be the price, right?
So what's a bayonet worth? Is it worth $400 dollars? Well no, that seems like a lot for a bayonet. I mean a lot of rifles sold back before the ban without bayonet lugs. So what about $300 dollars? Still seems high. Ok, well let's try $200. That seems high, but maybe....
Secondly, how much will it cost to restore the original pistol grip and furniture. Well a RSA FCG will run about $70 bucks (shipped). Then there is the new stockset, figure another $100. So we are up to $170 to fix that problem.
Well that's your price. Subtract the value of the bayonet, and the cost of replacing the furniture from $1100 dollars and you get $730. So a Mak-90 MUST be worth about $730. Otherwise all those pre-ban prices would be ridiculous.