If you're feeling DIYish you could try a solar solution. It's a housing with aluminum cans and a thermostat switch wired in series with the fan's power.
The company I work with had some some interns build one. Kicked out a fair amount of heat- likely enough for a single stall of a garage...
Another option to consider is called Nanospark. Works just like the above solution, but has more input/outputs.
I currently have it running 3 machines and monitoring another in my company's production area. Looking to incorporate my compressor too.
Setup is simple: control board > relay >...