Yesterday the Times reported on a textbook rental company that operates over the Internet at www.chegg.com. As of today, they're advertising the textbook for my Queens College Econ 206 class for a little over $30, and the textbook for my Grad Center Econ 71100 class for a little under $30.
As of today, list prices on Amazon for both of those are a little over $110 new or around $40 used, and a little under $50. The publisher also offers an eBook version of the former for $59.
Comparing these prices, one immediately recognizes the value to students of a smoothly operating market for used books.