I've got a buddy who wants to sell a shotgun. He doesn't know what to ask I told him I'd probably take it. But I got to find out what its worth. It is a Mossberg 500A, 28" modified choke. NOT the accu choke or ported barrel, so it must be older. What do ya think I should give him for it. I also got the serial # incase that helps. Any help would be appreciated. Thanks