I have a Left Hand 12 ga Wingmaster (2 3/4") with a 20" rifle sighted rem choke barrel and synthetic MC stock and fore arm. It was sitting on the shelf of the shop for close to a year and I was out the door for $250.
Depending on the barrel, in very nice condition, I would guess $300-$400 in my area if you can find some one looking for a left handed pump.