My gaming store answered me with prices for each book, so it helps. Pretty much everything Pathfinder 1ed is 5$ a book. Otherwise, it goes from 5 to 20$ depending on the rarity. My DnD 5e collector set can get 140$ (I paid 200$ for it, haven't crack any cover yet...).
It's really strange, because I don't need that money neither space, but seeing them in the shelves hurts me more than nothing, not too sure why, maybe because I know it worth something. I wish I had the time and the energy to DM a table, I really loved that. The vast majority of them, I never read them. So I wonder why I purchased them in the first place... :|