I use a ProCom propane heater in a well insulated garage and am happy with it. Its supposedly a high efficiency model from Northern Tool. I can still smell gas every now and then, but the CO detector does not go off.
My suggestion is a couple of the cheap milk house heaters if you have 3 circuits in the garage. Any 120v heater is going to about max out a circuit.
If you are short of circuits then substitute one of the catalytic Mr. Heaters they do a very good job.
Spend the left over cash on insulation.
Rick
