This has definitely taken time to workout and since we are fairly new to CM (this coming fall will be our first full year) I’ve had to tackle it a little bit each day.
I made a list (you could print it, too, I suppose) of the history module for my oldest kiddos and searched the library online. If they had it I marked it in pink, if not it got yellow, if we own it, purple. That gave me a good indication as to how many books I may have to buy myself or do Inter Library Loan for, especially if I felt they were too expensive and not sure if I want/need to own it. My 11 yo’s list wasn’t that bad. We own 3 of them, the library has 13 and the other 3 we bought. My 8yo’s was okay, too. The library had the first 8, which I thougt was great, then we had to buy a couple or do ILL, then buy a couple more then the library had another, etc. We ended up buying about 6 of them. It wasn’t because the ILL wasn’t working, but his books were fairly easy to get through, plus, I like to own some of our books, as well.
Having the books color coded helped me to see *at a glance* how close I was to needed to get that next book, library or otherwise. I also scour used book stores, the Goodwill, thrift stores so if I find one (even if the library has it) for .25 then I’m grabbing it:)
I did the same thing with their literature and science. I have to know in advance of what I’m doing and like to get my supplies way ahead of time and the only way I can do that is write it down (all the books) and search the library and go out looking for the books. I do use amazon, paperback swap and ebay, as well.
I have no idea if I helped to answer your question, but I hope so.