The new semester started just a few weeks ago, and between my wife's books for her classes and my books for my classes, we spent about $510 on textbooks for the semester. If we had purchased all of the books from Amazon.com, we would have paid about $675. If we had paid the list price for the books (as would have from our respective schools' bookstores), it would have cost us about $760.
Purchasing textbooks from a school bookstore, religious books from a local Christian bookstore, or good reading material from a supermarket or local bookstore may be convenient, but it is far from cost effective. Most of our books were purchased from Half.com or from Amazon Marketplace. My sister-in-law purchased a textbook off eBay for this semester and saved over $100 on that one Chemistry textbook! Oh, and by the way, all but a couple of the books we purchased were new. There isn't a very high percentage of difference between most used and new books in online marketplaces.
For frugality's sake, next time you need/want a book, don't just go to the local store and buy it. Be willing to wait a couple of weeks on shipment (plan ahead if needed!), and purchase it online. I recommend using GetTextbooks.com. GetTextbooks is a search engine through which you can search by ISBN#, title, or author. Once you have selected the book you want to purchase it compares online stores and marketplaces (including Half.com, Alibris, Amazon Marketplace, Bookbyte, eCampus), and displays a listing of the prices at each store. The displayed list is in order of price (lowest to highest), and displays the seller, new/used, price, shipping price, and the total you would pay. It's a great tool to quickly search a large number of online book sellers. If I had found this tool sooner, I probably would have saved even more!