I have done an initial test on single tube PCR, using a laboratory heating block set to 95C, with one side of the tube heated and the other cooled. On my first attempt, I tried heat in the side of the tube, but I didn't see any PCR product. On my second attempt,  with heated on the sloped bottom side of the tube, I saw a nice band after agarose gel electrophoresis. This was after a half hour of reaction time! 

I have now ordered a set of components for my first prototype. I will be looking at an Arduino-type setup, using either a ATMEGA328 or, if I can get the code optimised, I would like to use the ATTINY841, which should help keep the price low. I can't go much smaller, as I need at least 3 ADC's, 2 pins for serial (or V-USB), and 4+ DIO's.

I would like to use a JY-MCU bluetooth adapter for connecting to a server running on a PC, allowing a web interface to control the heating parameter of the PCR machine, but that would increase the price by a few dollars. Another option would be to use the V-USB interface, and have a wired connection, which would keep costs lower. Of course, I'm open to suggestions! Please let me know if you have a good idea on how to connect my PCR machine up *cheaply*. I need 2-way communication, to log temperature data and to set temperatures and temperature ramps. (yes, I'm looking at implementing Touchdown PCR :)