Instead of buying books, borrow books from the library.
Whenever possible, borrow your books instead of buying them.
The card to your public library is free and the libraries are generally well stocked.
In my city, the chain of public libraries is connected and the available books can be checked online.
If there is some book that I cannot find in my local branch, I can make a request online for it to be brought in from one of the other branches to mine which is very convenient.