I bought an organic textbook new, in the international edition, for much less money than the domestic edition, and it was identical except that the illustrations were black-and-white rather than color. It was for the India/Pakistan market, apparently; it had the price in rupees on the back.
I’ve had good luck with abebooks.com for some used textbooks. After purchasing some books brand new from my college bookstore for upwards of $100 each, I finally smartened up and get everything used or international now.
I also check and see if I really, really need the book, because there are instances where it’s not really applicable; the lecture notes and handouts might well provide everything that they are going to test you on, and the book adds little or nothing of value (especially if it’s poorly written, which is likely). Then, too, the library always has a couple of copies on reserve.