The reason textbooks are so expensive? In a nutshell: because they can be, and in some cases, because they need to be.

In fall 2014, the average student spent $313 on an average of 5.3 course materials, according to research by the National Association of College Stores. On a single course, students spent an average of $71.23, NACS reports.

And prices are changing every day, notes Peter Corrigan, CEO of The University Network, which recently launched a search engine that looks for the lowest priced books in real time. Below you can see how the average price of ten major textbooks fluctuated just over a week.