I have a Johnson Controls Refrigerator Thermostat. Plug the appliance of your choice into the thermostat, then plug the thermostat into a standard 120V outlet. An analog dial lets you set the setpoint temperature between 30 and 80°F, with 1 degree increments. The Johnson Control thermostat has a 3 1/2 degree differential, which means that the thermostat will shut the fridge or freezer off (stop cooling) at 3 1/2 deg below the setpoint and start the unit (resume cooling) once internal air temperature exceeds the setpoint
If you would prefer the digital version of the Johnson controller, Amazon has them for $68 plus s/h. I just picked one up the other day, best price I could find online.