Ok, here is my advice. It may not be legal, moral, or ethical, so take it with a grain of salt. This is what I did for most of my college years, when I was too broke ass to even really afford textbooks.
Don't buy the books until after your first class and you get a class syllabus. Then you will know which books are essential. Get together with people you know in that class, and pool your money together. Buy one copy of each book you need. Take everybody down to the local printer/Kinko's and make photocopies of the book chapters you need. Problem solved, for the most part, I found it cheaper to photocopy an entire book, and if I felt like being really fancy about it, having it bound into a notebook at the copy center (even then I would still often come out ahead by 50% at least). And if you were a really super cheap ass like me, you would scout your local library FIRST to see if there was a copy of textbook available for checkout before you even hit the bookstore.
Eventually I met up with four other people who were in the same major as I was in, and we almost always had the same class schedule together. We did this for at least 2 years until college was over. We must have saved thousands of dollars in the process.
How did we come up with this idea? We noticed that many of our textbooks, the professor would only use part of the book's contents, not the whole thing. It was frustrating beyond belief to have to pay out the ass for a book that we might only read one or two chapters in. We figured that if we pooled our money, and photocopied what we needed, we would save money. AND IT WORKED.
Edit: I should also add, when I went to college, there was no such thing as ebay, textbooks.com, amazon or barnes and noble. So there was very few options available then.