Garage Heat?

I have an electric 220 heater in my one garage that 16x25 and when it's on my electric meter will run the legs of the hamster I use a propane heater with the 15 lbs tanks from home depot in my bigger garage which is 25x90. i'm out there most weekends saturday and most of sunday I get 2 weekends out of one tank but that's cheap heat as far as i'm concerned