You southern boys are lucky!!! I use to Live in Austin Tx and Dallas, Winter was a breeze compared to Colorado, but .... no skiing.... so, I'll take the "champagne powder" winters here any day. CO gets more sunshine than Florida, but the chill in the air and altitude makes for an interesting winter, even if it is sunny.
When I was in Ohio I worked on restoring a car all through the winters - even when it was below 0 degrees F outside. The garage wasn't insulated or heated. A propane heater that runs off a tank like you use on your gas grill will warm the garage up (mine was 2.5 cars, and had a very tall roof) to at least 40 degrees F and let you keep working. If your garage is even smaller, with a low ceiling you should be able to do better than that.
One tank would last me about 15 hours depending on how much I had to crank it.
Now that I am in Florida, I wish it would cool off