Look on half.com. I used to find the "international" versions of a lot of books that were significantly (50-60%) cheaper. Content was the same, only difference was that they were paperback and the pages were like newspaper, but hey.
Buy used online Sell on Craigslist or online to keep the net very low Make sure you actually need the book before you buy it. Wait until the first classes and then decide. Don't buy on campus unless you have to Buy older versions of the books