One thing I learned as a college student was that the school bookstore is always the most-expensive option. At my undergraduate university there were two off-campus college bookstores, and they were both constantly cheaper than the campus bookstore for all textbooks. (Cheaper yet was ordering my books online from India, which is what I did most of the time.)
This semester I have selected a textbook that has an e-book option. When I notified my department that we'll be using an e-book, they told me I didn't need to give the particulars to the bookstore. But yesterday, the first day of class, the campus bookstore told me that some students are required to buy their textbooks through the campus bookstore, so I have to facilitate the bookstore's selling of the e-book.
I guess these students are using financial aid to purchase their textbooks. Still, this is bogus. When I received financial aid for textbooks, they gave me money and I spent it as needed. This meant I used some of it on Indian textbooks and the rest on food. If the concern is, "Well, if you can buy your books and have money left over that means we've given you too much money for your books," then require excess funds be returned. Don't require students to buy more-expensive books.