I bought a used copy for $5. I like using the library, but for books like this I am starting to do more buying so that I can keep the book for reference, let my wife or kids read it, pass it on to others at work or my extended family, etc. I don't buy every book I want to read, even buying used that isn't a good idea, but buying a book every couple months, especially if I can get it cheap, makes sense for me and helps spread good ideas to others when I pass it on.