my garage is a 40 x 26 x 12 ft sitck built. so floor to ceiling is about 13 ft.
it's insulated and drywalled. r19 in the walls and r33 in the ceiling.
i got a quote for heat, its basically:
30 ft Re-verber-ray 75k btu propane radiant tube unit installed for $3400, vented through roof etc...