I picked up a case of mixed size 16ga for $50, that is 250rds for $50, #6,4,2,SG,slugs, CIL, Imperial, Federal, unless this is the new issue Imperial ammo it is felt wad with no protection around the shot, spreads out a pile, not going to get you new prices for it. If it were odd shot sizes then it would be worth more but new stuff is between $13-20 a box, some would pay that but I think that is insane. One issue with old Imperial shells is the the brass splits, I have seen a lot of that. Have you inspected all the shells for splitting or just have the case and want to sell the boxes unopened?