Most other professors, especially within engineering were more than helpful with either giving out the ISBN so we didn't have to go through the bookstore, or in graduate school, had their own notes for the class, so a book wasn't even necessary. One class we were assigned two books that were available as PDFs from the authors, intentionally to be given away, which the professor pointed out. Thankfully in my engineering classes the professors have been helpful about allowing older editions of books or having a low cost alternative such as a compilation of notes. In my general education classes is where I've always encountered the incredibly expensive books that absolutely had to be the latest edition. I think it says something that the engineering books tended to hold up their value more than the books for those other classes, where a $130 english book ended up going back to the bookstore for $1.30. The engineering books were usually worth keeping too, once you got past the intro courses.
Oh, and the point I came here to make: Having a patent on an idea doesn't make it a good one.
*I'm going to keep calling it that, as that's the name on the splash screen when I load it.