Also hit charity shops near to universities at the end of the academic year. About 15 years ago when I was utterly broke I bought 20 text books (good ones like

Also hit charity shops near to universities at the end of the academic year. About 15 years ago when I was utterly broke I bought 20 text books (good ones like https://mitpress.mit.edu/books/introduction-algorithms-third-edition https://mitpress.mit.edu/books/introduction-algorithms-third... ) for .50p a book (they didn't know what they had so I gave them £20 for the lot instead of £10, would have done more but I really didn't have it).