When I was doing Algorithms and Data Structures at the University of Otago, the required textbook was Cormen's Introduction to Algorithms first edition. More than $NZ130 at the time, and we got a few weeks into the course before they told us we didn't actually need it for coursework, they just wanted to make sure we had a copy.

I see it's available for $US6.61 used on Amazon now...

edit: had the price about $50 too high.