I'm shocked at what prices people are asking. A good source would be icollector.com, various firearms auctions, look in past auctions and use Browning as a search word.
I have a remington 572 field master, they are going for 5-600. The Browning trombones have a following and average ones would go for that. Some collector will be along.and tell me I'm wrong. But I bet I'm wrong low.