My sources state that the electric rate is about 16 cents per kwh. The RV park may charge a small charge for meter reading.
Your cost per month will vary with uses.
Will you be washing and drying clothes?
Water heater...Gas or Electric?
Heat with Gas or Electric?
Water heater...Gas or Electric?
All this and more will effect your monthly bill.
Mine and yours are not going to be the same.
The last time I was on a metered site, It cost me about $3 a day for heating, water heater, cooking, lights, etc. No washer or dryer.