Startup Idea : helping college students save money on books

Going through college, I spent an arm and a leg of textbooks. Some of the textbooks I only opened once or twice, and could easily have done well in the class without it.My idea is a website/mobile app where college students can post class- and professor-specific opinions/data on whether or not the textbook is worth buying, for future students to use. Links to amazon or other cheaper sources to buy books can be provided too. A student hesitant to purchase a book for a class can go to that specific professor and class and see what past students have said, and decide for his/herself whether the risk of not purchasing a book and potentially be underprepared for the class is worth saving a couple hundred dollars.