<< well, if you buy it locally at least you can give it back >>
I don't know about your bookstore but ours buys back all the books whether you bought it from them or not (so long as it's being used again. if not there are at least 3 private parties around town that will buy just about any textbook at the end of a semester).
EDIT: BTW, I've found Half.com to be a great price to buy just about anything media oriented (books, movies, video games, etc). The prices are good because of the competition and half/ebay forces them to use a fixed shipping price on media items (keeps sellers from screwing you on the shipping).