The cost per kWH should be available from your power utility company for you to calculate the estimated $$. You might find this rate in your regular billing from them as well.
For eg: if the cost per kilo Watt Hour (kWH) = 10 cents and if your Pass is turn on 24/7 and it is rated at say 250 watt, the formulae that I will use is;
250W/1000W x 10 cents (per kWH) x 24 hours per day x 365 days per year = $219.00 or approx. $18.25 per month.
This is close to what Danlib1 has estimated as well...
Good luck.
For eg: if the cost per kilo Watt Hour (kWH) = 10 cents and if your Pass is turn on 24/7 and it is rated at say 250 watt, the formulae that I will use is;
250W/1000W x 10 cents (per kWH) x 24 hours per day x 365 days per year = $219.00 or approx. $18.25 per month.
This is close to what Danlib1 has estimated as well...
Good luck.