There are a lot of reasons why two copies of the same book would go for different prices
Are both version of the book new? If not, is the quality about the same? Maybe one shop has more copies of that book than the other. Perhaps due to who shops there, each store has different focuses on the types of books they offer.
It's also possible that one is just over pricing, or the other is giving you a good deal
I read one for Mean Girls a few years ago. The novelization of Battle Royale has a forward that talks about the concept. They are less common now because home media provides an easy way for people to reexperience the movie. That wasn't that case for most of the history of cinema