In the New York Times, an article about Chegg.com that rents textbooks to students. Actually, this is pretty much what happens anyway with textbooks being used and then sold on the second-hand market. This company just makes it easier to undertake that transaction without risk — especially edition risk. Interestingly, there is only so much in savings you can get.
A macroeconomics textbook that retails for $122 was available on Chegg for $65 for one semester; an organic chemistry title retailing for $123 was offered for $33. (Round-trip shipping can add $4 to a book.)
That said, many economics textbooks are out of date before they are printed so save where you can.