I live up on the Great Lakes and I use my garage quite a bit in the winter and I wouldn’t consider heating it. I did add a wood stove to the garage at my old house and hardly ever used it as it would take 10-12 hours to get it warmed up and by that time I was done working out there. It wasn’t insulated and part of the problem is heating the contents as everything in there is a heat sink. Another problem I found with heating here and there is it seemed to promote condensation on tools and such. I ended up doing something there that I improved on at with my garage now. I have a small heated workshop attached to the main garage that is about 16x12 and I have the walls and ceiling insulated with heavy thick foam. In mild weather a little electric heat cube takes the chill off and in cold weather it heats up quick with a small LP heater I run off a 20lb bottle. If I’m working in the main garage I go in and out of the work shop for tools and to warm up and lots of smaller projects I just do in the workshop.
If you really want a full time heated garage with full insulation there is only one way to do it. My good friend has a auto repair shop and he has hot water in the floor. It is beyond words how nice it feels in the winter and laying on the floor working under my truck is so nice I fall asleep.