Checking Kogan out and saw this which seems cheap enough! Thermometer could be used anywhere I guess but designed for fridge.
From the online manual
"The thermometer is incredibly easy to use. Simply place the display unit onto the top of your fridge and then place the cord with the small metal temperature sensitive tip into the fridge itself. The door can be closed with the cord being covered by the fridge seals. The seals will surround the cord and provide adequate insulation to ensure temperature heat-loss does not occur. The display unit can be affixed to the front of the fridge door if you so wish, using double-sided adhesive tape or sticking gum. (Adhesive agents not included)."
Cheaper on Ebay http://www.ebay.com.au/itm/New-LCD-Digital-Temperature-Therm…