I suggest going to Gun Broker, & doing an advance search for "completed auctions". That's guns that actually sold, rather than just asking prices. Of course thee will be some that might have sold for an uncharacteristically high, or low price, but a quick average of the in-between ones usually indicates value or what byers are currently willing to pay these days.
Most of the SS 45 Bisleys seen there will be the later Williams version, but I know no reason that an Accusport, Williams or other dist. version of the same gun would be priced differently.
Hope this helps & welcome to the forum.