I'm just now getting into home mead making, but I recently realized that my summer basement temperature of 72-74F is too warm for proper fermentation. So I set out to use what I had around the house to make a chiller for my fermenter.
I am a fairly accomplished DIY computer builder so I had a lot of spare parts left over from these activities. What I ended up creating was a liquid cooled jacket that I can wrap around a 5 gallon fermenter / carboy. The device uses a solid state peltier device, an air-cooled CPU cooler and a water-cooled CPU cooler. It circulates cold water through the insulated jacket, pulling heat from the fermenter.
It's not a particularly powerful device at only 120W, but it cooled my 72 degree must to 66 degrees in a few hours. This device could also be modified for higher wattages or even to circulate water through chiller pipes inside the fermenter. My goal here was to create a device that required no cleaning (does not come in contact with the must) and could be quickly deployed on any fermenter / carboy. In order to achieve these goals, the device's efficiency is reduced significantly...so there's definitely a trade-off.
The total cost of this device for me was about $20, but I used a lot of leftover equipment. For someone starting from scratch, the device would probably cost about $120.
If you guys would like more details on the consturction of this type of device, please let me know and I will post them.