Yep, kayak for textbooks. You can either search by book or search by school/course. If you really want to get angry, look up MATH 203 at Medgar Evers College in NY. A textbook with a list price of $174 is being sold for $330 new, $240 used - available from online sites for less than $10.
There are over 16,000 classes across the country that can save >$100 on their books. Haven't run the numbers yet but the use of custom materials/access codes has EXPLODED, which prevents savings.
We are diff than other comparison engines bc of that course search component. Most students don't realize how easy it is to save (it's surprisingly daunting for students to do this the first time), we facilitate that process.