Maybe I mentioned this before, but I just started making my own yogurt last month with my sister's starter. (don't know where she got it). I get fresh raw milk where I work for $4/gallon and make the yogurt the same day the cow was milked. It is so delicious!! like nothing I've ever had before and since i make it fresh it lasts for a long long time. It gets an inch of cream at the top too. I'm going to make more and start offering it to my egg customers for $3.50 a quart. (My egg customers are family and friends only).
Oh, and my sister taught me to fill an ice cube tray with yogurt dollops and keep it in the freezer. Then, I just take out one dollop, let it thaw, and use it as the starter again. (1 ice cube per quart). Works great and no messing with buying starter.