There is a brief article on textbook costs online in the Atlantic. Here is the link
With respect to textbooks, their size and their cost, here is an interesting situation that I observed when I taught a course in multivariable calculus. Many of the students had taken calculus in high school and only needed the “multivariable” part of the text. But the bookstore ordered the complete form (that is, single variable (not needed for them) and multivariable). It cost about $300 and weighed about 6 lbs. In its “multivariable only” form it cost $180 and weighed only 3 lbs.
Whenever I could override the standard order I did. That way, students who already had the complete edition – from a previous course – didn’t have to buy a new book, and those who didn’t have the complete edition could just buy what they needed. But wait. There is more. The editions would change. Then the student who even had the complete edition ($300) would have to buy the new edition – $300 if they didn’t know better, or I didn’t step in to fix things, or I wasn’t the teacher. Why did they have to buy another edition? Because the problems would change! That’s about it. I could not see anything else that had changed that really mattered as far as I was concerned – and the change in the problems rarely, if ever, mattered either.