Is this the black injection molded stock? If so $50 tops. But if it is a composite stock it will be higher. A pic would help and I could tell you more.
If the forearm barrel channel shows the webbing it is the injction molded synthetic stock. They are pretty flimsey and not in great demand. I have sold several for 30 to $50. What some people buy them for is to put on for a rough hunt and preserve their glassy Mark V Deluxe stocks.