When we were parked in metered sites and living in our motor home we used about 300 to 350 KWh per month - with no AC use. Multiplying the KWh by the cost per KWh will give you the monthly cost.
Our motor home plugged into our 30 amp outlet with the refrigerator turned off doesn't add enough to our bill to notice.
Clay WA5NMR - Ex Snowbird - 1 year, Ex Full timer for 11 years - 2004 Winnebago Sightseer 35N Workhorse chassis. Honda Accord toad.