I usually try to borrow books as much as possible - I read a lot, I'm broke, and books cost money - and I buy books that I can't find available to borrow anywhere. I also buy books impulsively quite often though, which is part of why I'm broke. And thus the cycle continues.

Edit: I also like to borrow books from the library as my first choice because I'm a big supporter of the concept of libraries, of people having access to entertainment and knowledge and community without having to pay for it, and I want to support that as much as I can.