A yogurt maker will cost you around $60.00. Most people agree that the Yogourmet brand is one of the best. You would need to purchase the freeze-dried yogurt starter, as well.
The crockpot idea that MoobyDoo posted sounds great, too! Why didn't I think of that?
I already own one of those!
I would beware of Activia yogurt!
We've had discussion threads here before on it. Most people agree that it causes D for them.
If you don't want to make your own yogurt, you might instead consider purchasing a high-quality organic brand like Stonyfield or another from a health-food store.