I'm a bio major, and most of our materials are "university specific." It's ridiculous. I usually save a little by buying what I can off Amazon.
I actually think I'm better off buying most of my books off Amazon and Half.com, then selling them back to the bookstore. I actually MADE MONEY last semester doing this (not counting unreturnable items, such as lab materials)
For instance, a brand new Organic Chem book lists for $213. I paid $110 for it on Half.com. I could have rented it from Chegg for $62 a semester. But, I will use this book for 2 semesters, so it would actually be cheaper for me to buy it, then sell it back.