A sousvide controller project based on a Arduino + open source PID libraries.
Solid state relay ~8 USD
Heatsink ~6 USD
DS18B20 ~10 USD
4,7k resistor ~0.01 USD
Arduino Duemilanove ~ 30 USD
The heating source is a slow cooker of basically any "dumb" type. No digital controlls just a "Low, High" heat setting that turns on and off if you pull the plug out from the wall. I used Hamilton Beach 6 Quart ~ 30 USD
Extension cord ~4 USD
Total cost: ~90 USD
Feel free to fork, reuse and play with it.