Lots of ways to judge value. Probably the best is to do the following:
Go to sites such as dealer sites, Simpsons, or Ralph Shattucks, or Randy Beesler's, and others and you can get a good feel for prices. Then go to Gun Auction boards and see how much guns go for. Then lastly go to larger gun shows such as Reno and you can see many prices there.
If you showed many pictures and a good description, you could get a very rough value here, but it would simply be a guess, as judging it in person is really needed.
Ed