Your gun is the Tobin Black Diamond Grade #55, which in their Canadian catalogue of 1911 was priced at $35,or $55 with single trigger and auto ejectors. Because your gun is marked G.B.Crandall the gun was made after 1922. At this time,Mr, Crandall took over the business.He built a limited number of guns from the inventory of parts remaining from the defunct Tobin Arms Company.
The Tobin factory still exists in Woodstock but sadly selling domestic light fittings rather than shot guns.I have seen Tobin guns sold in the price range of $200-1750. High grade guns are seldom seen. $250-300 would seem appropriate for your gun.
