Most of my books are from a library booksale, or other second hand places.
And with books you have read, you can swap them easily. Look for some readers who have the same taste around your area, or e.g. a bookcrossing shelf may be helpful.
I also swap books I’ve read with friends, and use bookcrossing and goodreads for book swaps. With those it helps a lot to find others who have a similar taste in books than you do.

As other commenters have suggested, you can also help by making donations to the library. You can donate materials or money but you can also donate time if you don’t have things to spare. Library volunteers can help in myriad ways.

Short-sighted me-first thinking has gotten our nation into this financial mess. It won’t get us out of it. Don’t just figure out how to meet your book needs, but see what you can do to keep your library from dying!

It isn't that your library is letting you down, we are letting our libraries down! Libraries are one of the last free resources that are there for everybody. Instead of thinking up even more ways to get books (although I love cheap books and read like crazy) you might want to try thinking of 'what can I do for my library?' If you bought and read a new book, have you considered asking the librarian if they would like it for the shelves? Have you donated money towards the library fund? I even overheard my librarian talking and some libraries get state funding based in part on circulation of books. If so then you need to USE the library as much as possible. Ask the librarian what you can do to help. If you love to read and have some spare time, perhaps you could volunteer there. If you have a magazine subscription that they library doesn't ask if they would like your copies to set out and donate them as soon as you are done reading them.

We need to keep our libraries viable into the future. I realize that many don't read even though they can, which to me is worse than those who don't read because they can't. Reading stretches the mind and not everything is on little electronic devices nor will it ever be.

However one way we try to keep it that way is to donate every book or movie we need to get rid of to the library. Things that would take up space in our house, help keep their shelves stocked, or offer a chance for them to earn money.

I also return the books we buy from their sales, it is very rare that I would want a book to take up space in my very small house. A nice fluff fiction book is fun for a night, but after…it needs to go. That way the Library made my 50 cents, and can possibly make it again.