It seems like this depends on the universities (and maybe also on undergrad vs grad), but I've done my masters, and am currently doing my phd at an Ivy in the US, and I've been pleasantly surprised to find out that we are almost never required to buy any books. Often, the professor uploads a set of very comprehensive notes accumulated over the previous years to complement the notes we take in class. It's happened (three times out of maybe 8 classes) that the professor is writing his own book on the subject, and so is giving us free copies. So instead of requiring books, the professor indicates which books are interesting/useful references on the subject and puts them on reserve in the library for the students of the class. I think it's a good system.

One thing though. This is doable in science because, well a theorem is a theorem. But about humanities where you have to study specific texts or corpora? I don't think there's much choice there..