Only recently has this monopoly been broken with the advent of online textbook purchasing, and prices are a bit more reasonable on the new prices. They still rape you on the used purchase/sell-back end but that can be circumvented if you keep an ear out and find people who just had the class and you're about to take it. Cut out the middle-man and both sides are happy. Higher learning has become such a racket driven by lust for profit.
Recently taking more classes we used e-book versions which I say was even more of a rip-off. The e-book cost about 40-60% of the dead-tree version, and they revoke access after about six months to a year, and of course you can't sell it back at all. Maybe I am weird but I prefer to keep my textbooks as reference and refreshers.