Build Your Own Yogurt Maker, Sous-vide Cooker, and All-purpose Fermenter for $40

I make a half gallon of yogurt, twice a month.  I like making my own yogurt for many reasons, but it's a bit of a pain.  Since I make large batches, I can't use a standard yogurt maker.  I often get distracted and over-heat the milk, and the method I use to incubate the yogurt is wildly inefficient (my beloved Excalibur dehydrator).  I also need a constant warm temperature for various other fermentation projects, and that's often difficult to achieve with the tools I have.

I finally found a better solution: a temperature controller that accurately regulates the temperature of a slow cooker by turning an outlet on or off.  I simply set the temperature of the controller, place the temperature probe into the slow cooker, and plug the slow cooker into the temperature controller outlet.  The slow cooker then stays at whatever temperature I want.  Here's what the temperature controller looks like: