Those prices are your supposedly 'free-market' system at work. They charge that much because they fucking can. For all intents and purposes, the number of college students is static - it doesn't follow the market. As such, it isn't really subject to the mysterious workings of supply and demand. Say they charge you $400 for a book, what the fuck can you do about it? Drop out of school? Refuse to buy the book, ie, fail? You can't do shit - they have you by the short and curlies. And don't even think about complaining to your professors or administrators - they have sweet little kickback distribution deals with the book vendors, which basically locks them into a contract.
Like Skyman's oceanography book - of course the professor is going to assign his book to his class. And fuck how much it costs - more cash for him! And used books prevent you from spending more fucking money. What kind of retarded publisher would release one edition of a book and have it recirculate through the college for 20 years? Fuck that, come out with a new edition every other semester. Or even better, include a cd-rom, or a solution manual, which makes the book absolutely worthless the moment you buy it! Besides, everyone expects textbook prices to be high, so constantly raising them is totally acceptable.
Get used to high textbook prices, because they ain't going anywhere. Unless there's a revolution.