I think it is much easier to evaluate the "going rate" for two particular guns going into a trade. After that evaluation, which both sides should make, the two parties should figure out for themselves if a trade is worthwhile. Hopefully both parties benefit from the trade.
All my firearms are unique. They each have a unique number on them. Some call it the serial number. Me, I know it is the only one that Colt (or whoever) has or will make with that unique number. A rare one of a kind...each and every one of them. Therefore it is worth whatever I ask.
Now of course your gun is just a run of the mill average gun with nothing special about it. Therefore only worth what I offer you.