I don’t eat that much yogurt, but if I did, I would definitely look into making my own, especially with an heirloom yogurt starter. This is a bacterial culture that you can use over and over to make yogurt. Amazingly, these bacterial cultures originated years ago in countries like Finland and Bulgaria, according to NPR. They have “been around for a very long time and has been passed down for hundreds of years.”
To make the yogurt, you add freeze-dried starter or a spoonful of yogurt to milk.
The only catch is that you have to continually make a new batch of yogurt every week to keep the culture going. If you don’t, it dies. So to make this worth it, you could have to be someone who eats that much yogurt every week.
The Frugal Girl estimates that she saves hundreds by making her own yogurt: “Four quarts of grocery store yogurt per week would cost me between $416 and $624 a year, and this yogurt (from milk purchased at $2/gallon) costs me a measly $52 a year.”
ETA: In the comments, Ralph Lowd explains that he freezes his yogurt starter:
I take a piece of plastic wrap and place it over two egg cartons creating 24 depressions. into each of these I spoon 1 – 2 tablespoons of yogurt and put in freezer. When frozen I individually wrap each ball of yogurt putting all in a zip-loc baggie and put back in freezer. I now can use one yogurt ball to make a batch of yogurt if I don’t currently have live yogurt in the fridge. I also can use some of my starter for recipes that require only a small amount of yogurt.