I had to take a philosophy course in college back in 1991, and the only class that fit my schedule was taught by a guy who had "his own" book out, that was the required text. Basically, it was a compendium of essays by the great philosophers, broken down into chapters, with italicized commentary from him before each chapter, consisting of one paragraph, to up to a page. He perhaps actually "wrote" 10 pages out of the 300 page text.
Cost for the book was $67, that was 10 years ago.
Textbooks are the biggest scam going. Do you actually think Calculus today is any different than 10 years ago yet typically each edition of Calculus lasts only for about 3 years until a new edition, with minor changes comes out. Why the new editions? Calculus doesn't change from year to year. The reason is to make students buy more new books at inflated prices. And the reason why this scam works so great is that the students are captive consumers. They have NO CHOICE but to buy those textbooks.