A good portion of the homeschool books we have purchased over the past few years, I have been able to find used. Used = cheap. There used to be a great homeschool bookstore about a 1/2 hr from our house...they sold new books plus used and I always found a lot of great deals there.
Until they moved to a new location. Actually their first move was not too bad - it was further from home, but they still had a nice selection of used materials. Then after about a year, they moved again. Closer to home - but when we went there today, a very poor selection of used books. Sigh.
I did get some good deals...I spent about $40 on curriculum that had a retail price of approx. $140. So I'm happy about that. But as I said, the selection was poor and I'm still on the hunt for quite a few books.
There is a used curriculum fair that I usually attend in June, but I just realized that it is on the same date as an out-of-town wedding I'll be attending.
I still have a few months left to look but now that I have started hunting - I want to get it all done quickly. I do check out eBay for books, and did find one tonight that I bought, but the problem with eBay is that you pay for shipping, you can't physically look through the book to make sure it's exactly what you want, plus you have other people bidding against you. Also a year or so ago, eBay quit allowing the sale of answer keys.
In case you are wondering, I use Saxon for math and A Beka for all the other subjects. I'm not too crazy about A Beka, but I continue to use it. Some of it is useless and boring. I need to keep reminding myself that I do not have to follow things exactly. I don't even have to give all the tests or reviews or assignments. If the next chapter is on birds and my daughter thinks it's boring - why not move onto something else. Sure kids need to realize that even if something is boring they may still have to do it - but there is plenty of time for that later! Now if my kids didn't know a cardinal from a duck, that would be one thing. But if the kids already know something - why spend time on it over and over.
I do supplement all the subjects with whatever we find at the library or from various other resources. If the children are interested in a subject that we are not currently studying - it's easy enough for us to find information about it on-line or at the library.