Should I Buy A Prep Book To Study Over The Summer For AP classes?

Yes! I don't see why not. I highly recommend PR because the tests are not unnecessarily complicated and they're relevant. You'll get a glance of the materials before everyone else and you'll feel prepared for the course. Plus, it makes understanding lecture a lot simpler. You'll also be using it throughout the year to help you prepare for the chapter tests and homework assignment. If you're planning on getting all of those books, you can order the used ones online. They're cheap and I found that the newer editions aren't necessary. You can buy old books. The publisher basically reuses the same practice tests so there's no point of getting the newest edition.