If you have not sold back your textbook yet, you might be able to collect more money for it if you bypass the bookstore. Their price to buy back your book is pitifully low -- I heard $21 -- but they will then turn around your copy and sell it at an outrageous $133. Go ahead and look it up on their website!
It really burns my grits.
So if you sell to a friend or roommate in August at $60, your friend or roommate will save significant dineros and you'll have more than the bookstore will give you at buy back.