Well, that website doesn't provide curriculum, per se. It offers links to resources. Some of those resources are free, some are not.
We're using Singapore Math, our local library and free sites on the Internet for our curriculum. (Just double-check the sites for accuracy--remember that anyone can post anything on the Internet and claim that it's true. That doesn't mean that it is!)
Our costs are very low, and we can be sure that the material is both interesting and sufficiently challenging for DS. It's not as easy as tossing a workbook at him, but it is a lot more varied and interesting, as well as a lot cheaper.
I recommend that you check out E.D. Hirsch's "What Your __ Grader Ought to Know" series. Pick the grade level you want, and follow his basic outline. The books are available used for cheap on sites like Amazon.com, and they're very useful. It's my guide for curriculum and coverage.
