The most I ever spent for a single textbook was $130. And that really wasn’t that bad, since I was able to use it for all three semesters of calculus. But I did have one course for which the professor used three different books, and the total for that class was up in the $200 range. That hurt.
The textbook world was a distorted market for a long time: if you wanted to do well in the class, you had to pay for the books the professor used, sold only in the campus bookstore. The textbook publishers and bookstores took advantage of their captive customers and jacked up the prices. They also found ways to issue a new edition every few years to reduce competition from used booksellers.
Today, that old textbook-purchasing model is being blown apart. Harry Painter describes this disruption in his article “An End to the Textbook Racket?”.