Since at least some university professors should be able to write a good textbook on the subject they teach, the university should give them a semester or two off of teaching classes to write one, give the professor a little royalty ($1/book?), and then publish and sell the book at cost. $15 to $30 per book. Then don't change it until necessary (calculus could be the exact same book for decades) so that even cheaper used books are plentiful. Many universities even already run their own publishing houses.
I'm not sure where the friction is that prevents this from happening? University presidents like to have fancy dinners with textbook publishing house CEOs?