priceretriever compares various rental book retailers including b&n. Ive not been very impressed with rental prices myself. Used is often less expensive in the long run.

Check out a Chrome Extension called priceretriever, it compares prices while you are on a college bookstore website. Sort of like invisiblehand or kayak for textbooks.

priceretriever.net compares textbook prices (including rental). They have a browser extension that will automatically compare prices on college bookstore websites. Really though, rental is usually more expensive than buying used and reselling.