You would be surprised how cheap you can find used books. I find 1 cent books on half.com all the time.
I set a goal for finding all of our Module 5 books for $100 or less, and this includes books on the reading lists for three age groups (1-3, 4-6 and 7-9). I have 5 children using the Module, so that is a LOT of books. If you needed just one or two age groups, you should be able to find them for much less.
I bought more than 30 books for right at $100. Almost all of them are used. I still have a few we don’t have and maybe we won’t have, but I have already looked on the SCM bookfinder and a few other sites and found some worthy substitutes. That is the thing: you can always substitute.
I like the library, but I agree with others that I want to have the book when we need it, and that may be for more than 3 weeks (how long we can have it checked out from library).
I also found quite a few books at a local used curriculum sale, so if there are any in your area, they might be worth a look. I found A Child’s History of the World, which was on my long-term book list “if I find it cheap enough”, for $8!!! It is like brand new, so I bought it to have on the shelf.
Oh, that is another thing. Keep a running list of books you are looking for. You might happen upon a used book store. I have done that before too, and the owners can usually tell you right off if they have a book on your list. And if they have several, don’t be afraid to negotiate. Used items are usually always negotiable, especially if you are buying in bulk.
I would say set a goal of how much you can budget and just start looking. You might be surprised. Oh and if you buy new, try to buy those from Amazon on the 4 for 3 promotion. This helps too and group them so that you are buying 4 books of same price or close to it. This way you buy 3 and get 1 free.
HTH