It depends on what your electricity costs per kwh. We pay 6.3 cents here, so a 5kw electric heater, running all the time, would cost approximately 31.5 cents/hour, or $7.56/day. My heater runs about 45-50% of the time to keep my garage comfortable to work in (55-60*F) , so between $3.00 - $4.00 per day.
Here it's 11.5 cents/kWh - so it costs .57 per full hour of run time. That's if running continuous, which it does not. How much depends on the temps and the thermostat setting.
thanks fellas.....I live in Wisconsin and right now it's about -10 with the wind chill....I'd use it to **** around a bit in my little shop and thaw my truck and plow after a night of throwing snow....