I run a 120-volt quartz two-element ceiling-mounted heater that I bought from Lee Valley for $60. My shop is 20x20 with 8' ceilings; 6" insulation in the attic and 4" in the walls.
Set on high, it kept the shop at 48º overnight in -18º temps last week. That's not a pleasant working temperature, but it keeps the glue from freezing. Usually, I can maintain 60º during the winter, keeping one element on overnight and switching to 2 elements in the morning.
I live in south-central Michigan.