I will suggest half.com, eBay, or amazon
. I prefer eBay coz I will see the exact picture of what I am buying and not a stock photo or tell the seller to send me the actual picture of the item I will be receiving. I purchase textbooks in a like new or very good condition on eBay since there will be no highlights, ripped pages or sorts on them so as to get a good value for my money.
The best part of it is that I sell them on eBay after the end of the class for virtually the same price I got them or more. I have never ran at a loss on the original price of purchasing these books so far.
I also do not rent textbooks because I can not get my money back afterwards.
I am not on financial aid so this is my own little way of saving while investing in my career.