The professor that taught my algorithms & data structures course said if we were going to keep one book it should be the one for that course. I followed that advice and it's the one textbook I still have. It's been 8 years since graduation and I haven't opened it once. I tend to just read Wikipedia if I need to understand a particular algorithm or data structure.
The best investment I made in textbooks was the class that wanted a Schaum's Outline book, $15 brand new and still a book I use for occasional linear algebra reference.
Don't you have university library? I did most of the recommend readings through my studies and found them all there (excepted for one). Ended up being a two reference books which prove themselves to be worth it.