I was unsure about how much it costs to operate the block heater on an '82 300D, so I bought a LaCrosse cost control meter. The heater draws about 450 watts, so plugging in for 2 hours plus = about 1KWH. Here in NH that means about $.22. Well worth it for an easy start even at 5 degrees. The meter cost way more than a year's worth of plugging in the heater.