I've seen them go for that, but it would be very hard for me to hand over that much cash for a MAK90. Don't get me wrong - I own a MAK90 and love every inch of it. They are great specimens of the AK. Gunbroker has them for sale on there for $499 and up, but if you watch them long enough, you will see that they don't actually sell.
I think a more fair HIGH price would be $400 to $425. And that would be for a pristine, Unfired, NIB w/all the accessories original to the rifle.
My target price since it sounds like all of it MAY not be original would be more like $300 to $350. Someone can correct me if I'm wrong, but if it doesn't have the thumbhole stock - it isn't all original.
I know some will disagree w/me on the price. MAK90's do draw a premium in some cases, but I just don't see that it is worth it. I'd be looking at putting a little extra and shopping for a Vector or Krebs AK.
If you are dead set on a MAK90, be patient and look around. I found my MAK90 at a local pawn shop for $250 just around a year ago. It was brand spankin' new, unfired and in the box. Someone had brought five of them in and pawned them. I was lucky enough to buy two of them. Deals are out there...........
DK