Hi, Cathy. If you watch the show a lot, you will see that they only do big projects. There are some other shows that do show small projects so check HGTV and TLC for these. Location will be a big issue.
As I understand it, the work on the houses is not free either. I believe that the homeowner basically pays for the labor and some materials. Other material is "donated" but the homeowner has to pay income tax on the full retail value of the material. That is some savings, but as you could shop for some of these items and get them cheaper than full retail price, that is not as much a saving as you might think.
If you look at shows where they have gone back to a house that was done before, a lot of that beautiful furniture and the decorator items are missing. Those are loaned for the photo shoot and the wrap party. You might be able to get a few bucks if a magazine picks your project for a big photo spread.
So you are left with making money the good old American way--suing somebody--if you want your project done free. But that's another story.