PID Controlling a Peltier based cooler

Hi group,

I have a small cooler based in peltier to control the inner temperature of the chamber. I want to use the thermal module (with peltier, fan and heat sink) to control the temperature in a aluminium block of 7x7x7 centimeters,the setpoint is 18ºC, the room temperature is 25ºC. (I must take appart this parts and include in my design). The cooler have only 'heat' or 'cold'. Heat is almost 40ºc and cold is almost 0ºC, the product have no other temperatures.

I want to control the temperature with a PID digital controller, model CAL 3300 (http://www.cal-controls.com/products/3300m.php), my main question is where to intercept, cut and connect the wires to the controller. So please view the picture below and do not hesitate to ask me any question that you may have.

http://www.biolabware.com/Peltier_Control.jpg

I have not enough budget to purchase the separate parts for the peltier and the power source, so please do not tell me 'go to the electronic store'

Thanks!