I use amazon as a poster above also mentioned
it's part of my cheapo strategy
I am fortunate to have 3 libraries (but they have 4 sources of books PLUS several resources for me as being legally blind, so I put holds on all my books as they are released, so I can read them, but I actually prefer owning my favorite 5 or 6 authors in book form so after 6 months or so I go to amazon when they have an "eligible for FREE Super Saver Shipping on orders over $25" sale and go through the used books
I have sometimes gotten 30 books for close to $50 and all books were in great shape I actually rarely selected the cheapest book available...