For almost all of your 100 and 200 level courses, and some of your 300s and 400s, you can probably find the international copy of your textbook on eBay. These versions of the textbook are paperback, intended for resale in developing economies and, for that reason, are usually about a quarter of the price of their University store hardcover equivalent. Simply search for only the ISBN in eBay and look for the result that says “international copy” in the description. Make sure that the seller has a decent rating before placing an order.