How to go about lowering the prices on my college books?

College books are expensive! I need 3 other books, and I'm looking to go to the book stores near my school. They both have the "cheapest prices guarantied!!" thing advertised. I went in and tried to haggle, and did but the prices were too high still. So I went home and looked the books up online and found them like 40-60 $ each. Question is, can I go in with the printouts and ask for them to honor there advertisement and give me a cheaper price than that? I used amazon and brains list for prices and printed the things out. Can I use this? Threaten with the better business burrow if they don't?