Arduino Thermostat is open source, meaning access to lifetime design. While Chinese versions are cheap, the Arduino route guarantees 10x the life, and as such, is a lifecycle cheaper And more environmentally friendly option. Arduino is $3.5, relay is $1, probe is $1 - so double the price but 10x the life mi us the waste.
Let's Make this Exciting
To keep cost down while keeping state of art funtionality via smart thermostat features - we can use an Arduino with wireless communication to control the thermostat with an Android phone.
Open Source Industry Standards
- Arduino thermostat with wireless Pi controller - 
- How to control your Arduous no with a cell phone - 
- $3.50 for Arduino Nano -