At the very least, should your friend refuse the money, you could give an amount of his favorite beer or liquor equal to the money you would have given him as a "thank you."
I figured I would give you the blue book values. You can go from there for what you think its worth. Used guns that don't have original box normally top out around 90% in good shape. 95 and 98% are saved for guns unfired in boxes. I'll give you all the prices anyway.
These are the prices listed under Ithica/SKB for the model 200. There are small differences in prices between a couple variations but for the most part they are pretty close. Hope this helps your decision.