Cooling thermostat

Can anyone recommend an affordable cooling thermostat? I need the exhaust to kick on when it gets hot and turn back off when it cools down.

I have found a couple expensive options that operate at line voltage, but nothing cheap or ideally suited.

Thanks for your help.

Bump No suggestions?

When my fan runs constantly it causes my box to get too cool. When the fan doesn't run at all it gets too hot. Thus the need for the thermostat.

One more try before I give up. Bump.

I realize your post is 3 years old, but maybe this will help someone. A cheap or possibly free thermostat can be had out of an old window unit ac. Just put it on one side or the other of the power going to the fan and you have a thermostat. I bet if you go by an appliance repair place that works on window units they'd give you one. This would work on 110 or lower voltage for sure.