VINTAGE WGP SNIPER PUMP ONE OF THE FIRST CHECK IT OUT - eBay (item 230307904591 end time Nov-22-08 12:23:16 PST)
Here is one on Ebay starting at $200 no bids yet.
Old marker prices are down lately but see what it goes for, that might give you a better idea what you can get for yours.
The polished barrel and drilled stock lowers the value.
Good luck.