I often wish there existed a 'student course materials bill of rights'. At a minimum, it would require professors to indicate which version(s) of the texts are acceptable, and would require them to provide this information ~2 weeks before the start of the term, allowing students time to order used books online.

The current-1 edition of a textbook, purchased used on Amazon, is often 25-50% of the cost of the new textbook in the college bookstore...

Of course, open-source textbooks would be even better.