But first, I'd like to address some "issues" you might have about our money-saving suggestions:
Firstly, you have to get over the idea that every book you read you'll want to hold onto for ever and ever. Yes, people like to collect libraries. I certainly do. And the two most commonly given reasons for me doing this are: "I'm totally going to re-read this book" and "I like having them around to lend out to others to read!"
These opinions of mine are BS.
You're not going to re-read that Dean Koontz book, and your friends could care less about what you like. (Especially if you like Dean Koontz.)
Secondly, you have to get over the "Ick Factor" of second/third/fourth-hand books. Though you can never know what the last guy reading that book had touched before reading it, I doubt it was hazardous waste. (Unless there is tell-tale evidence stuck between the pages, that is *shudder*.) You'll be okay if you'd just refrain from licking the book.
If you're really concerned, or if your name is Howie Mandell, just stock up on Purell.
Now, with your worries assuaged, here's some places to get cheap(er) books: