Just by averaging the internet prices your friend got, as you put it, hosed.
If you take into consideration, gun show, gun shop, pawn shop and deals from individuals; he still got hosed, only harder.
In the condition you describe, it is worth $50-80 tops and you would have to look hard to find someone knowledgeable who is willing to pay that much.
If you don't believe me just look at the Marlin shotgun page on Guns America as an example. Marlin shotguns