Finding and comparing prices with your local bookstores is easy. I searched our local college bookstore website as if I was a student taking a certain course and got a list of the required books by ISBN. After noting their purchase and rental prices, I copied the ISBN number for the required book and pasted it into the search at CampusBookRentals. I entered the rental return date as one week after the end of the semester. The price to rent a used version of this book locally - $163.58. The price to rent this book from CampusBookRental for the semester - $14.60 with free shipping both ways! Speechless!
Now keep in mind, this is a new website so it appears that there is not a lot of data yet in this part of the site about the potential demand for these books and the site may tell you its not worth sending your books in because the data isn't there yet. For instance, none of the required textbooks for the classes I looked up above showed as having rental demand or value. However, I know they are the currently required textbooks for the classes currently being offered at our local college so there will be people looking for them if they are made available.
Here's more about how it works.