If your garage is a "working" garage, as in you have your car in there and the doors are opening and closing all the time to allow your car in and out, then heating it, and keeping that heat in there, is going to be tricky, especially in the cooler months, and even more so if your cooler months are brutal. That's one thing to consider.
If it isn't a working garage, maybe your car(s) are constantly parked on a driveway for example, then the next thing to consider is, is your garage very well insulated, especially draught prove around those big doors?
And also the size of the garage. Our UK garages tend to be small spaces, enough for one car and a bit of shelving on the walls for storage. Whereas US garages for instance, can be huge sprawling garages. Bigger = more expensive to heat.
Ideally, cost wise, you'd want to be heating a small, non working, well insulated garage. A small electrical heater with a thermostat would be ideal. Set it to 25°C for example. Once it heats the room to said temp it will switch off. Once the temps go down to say 23°C the heater will automatically come back on, and so on and so forth. How costly using an electrical heater will be, given the energy costs, relies solely on how insulated and toasty you can make your garage.
And then, depending on your summers, that well insulated space could work against you. It may become too hot. Leaving the doors open and having fans in there may help then.
That's how I'd do it given the criteria I mentioned. But your criteria could be totally different and my suggestion simply would not be cost effective.
I'm sure others will chirp in, good luck.
