Look on ebay. Lots of old wood, cheap- cheaper than new ones. You can get an idea of what things are worth. They are only "worth" what someone will pay. Prices for run-of the-mill have actually gone down, since the internet.
At shows, you will pay a premium. Some guys are so high, they have the same things for sale, year after year. I think they are just showing off their collection. My best scores have come from garage sales.
My advice is decide what you will collect and become familiar with it. If you want to play with the big boys for stuff in the box, $300 and up for one piece, you HAVE to know it.
Plenty of books, websites. Prices in books are usually high because the guy who wrote the book already has it.
You can buy lots of fair conditions for less than half of one good condition. Remember, you can only display so much. Do you want ten Chevettes or one Corvette?
Be careful, if you want fish decoys. You need a mentor for that. So many fakes around. They are more folk art to me, but guys go crazy over them.