I just remembered a little test I did a while back, had my dad's 84 plugged in, and watched the meter. By the numbers given on that, it was on track to cost about $30 a month if it were plugged in 24/7.I read the meter at the same time 24 hours apart, and our power is about 10 cents a kilowatt/hour if I remember correctly.
They make little meters to check electrical usage, just plug it in then plug in whatever, tells you how much it uses. Bought mine for $45 and I found out I needed a new deep freeze pretty badly. Kinda nice to know what uses what.
Ohms is nice for estimates, but without knowing the actual resistance and current, it is an educated guess. Ratings don't guarantee usage. I do know what themeter said for usage, so that's why I went that way. (Not to mention, forgot to try figuring it by Ohm's law...)