About 64 cents of each dollar you spend on a new textbook goes back to the publisher. Your bookstore receives just under 23 cents, the author 11 cents, and that extra penny or two goes to the freight company that delivers the books to the store. You can find a more detailed breakdown here: http://www.datc.edu/files/datc/departments/bookstore/textbook$.pdf
The burgeoning used-book market--made even more widespread as the Internet grows--has made it more difficult for the publishers to sell new books. To combat this, it has become common practice for publishers to issue new editions of textbooks every three or four years. Some subjects, like political science and computer programming may warrant an update that often, but many do not. By issuing new releases, publishers make it difficult for students to find used books to buy. Another growing trend is for the publishers to "bundle" the books with software, web codes and workbooks. If, for example, a new textbook has a one-time-only web activation code, the initial user will have a harder time selling the book into the used market.
The used-book market has grown exponentially. Students are able to go online and purchase a book from hundreds of miles away with the growth of the online market. Used-book sellers, whether private individuals, internet providers, or physical used-book stores do not pay a fee to the publisher for the reuse of the product, prompting the publisher to increase prices to compensate.
Publishers readily give free copies of new textbooks to professors in the hope that the teacher will choose that book for his or her course. Professors are sometimes not aware of the price of the book when it is new, or what the plethora of other materials bundled with the book will add to that price. Professors who are authors themselves will naturally assign their books as required reading--not only because they believe in their books, but also to reap the royalties
The cost of raw materials to make textbooks has been rising steadily. Paper, storage space, printing inks and employee salaries have increased, adding expense to the publisher. Unlike mass-market paperbacks, fewer textbooks are published in the quantities that make large press runs feasible. Spikes in gas prices make shipping books more expensive. Like most products, textbooks have two entities expecting to make a profit--the publisher and the college bookstore.