It's probably more than 50 dollars for a textbook but absolutely, they are still paying exhorbitant fees for the digital works, and buying new ones when their old ones are still good. It's not like there are advances changing these subjects, math, history, economics, political science, you name it, buy it once and own it, and reprint the same book. Print an addendum to add new information if you want. But there is no reason to get a new math book every few years. Algebra hasn't changed one bit in lifetimes.