Homeschooling on a tight budget. Here are a few suggestions:
If you like the Charlotte Mason style, you can use http://amblesideonline.org/ , which has free curriculum, book lists, suggestions for how to implement various studies, and a host of other resources. This is what we use and my children love it.
If you’re interested in another learning method, check out yahoo groups for that. Often you can find used materials and suggestions and/or advice on how to implement different techniques for different learning styles.
The library is a wonderful tool. You can get unit studies, books on tape, tons of classics, science books, etc. Often libraries (at least the ones I’ve been to) offer special teacher cards that allow an individual to check out more books and (sometimes) for longer periods of time.
Used bookstores. Most used book stores have an “education” or “family” section, where you can find all sorts of quality used homeschool books. We visit the used bookstores every month or so and can usually find some great treasures.
Contact local home school groups. They can tell you when used book sales are and help you with any questions or requirements your state may have. You can also find out about home school sports, field trips, and a host of other things.
I can not stress a home school group enough. Not only will your grandchildren be able to be involved in all sorts of activities, but their parents will not feel so alone or isolated. A lot of people home school and can point new home schoolers in the right direction.