I finally got my account validated, so heres my first posting:
You wrote that you heat your home with wood.
If you have hydronic heating in your house, you could consider drawing well insulated pipes from your house to your garage and installing an air handling unit.
That way you could benefit from the cheap heat from wood.
You should make a small bypass in the garage keep some circulation in the pipes to avoid freezing when you are not heating the garage in the winter.
I have no idea what you have available in the US, but here in Denmark we can buy ready-made plastic pipes with two, three or four insulated pipes inside, designed for underground use.
It would be a real luxury to have hydronic heating + hot and cold water in the garage.