jerboys, are you planning on weekend camping or long term staying at one campground?
Most campgrounds charge a set campsite rate for weekend camping and/or only a few days, that won't change if you use a lot of electric (usually air conditioner running).
Some campgrounds will charge extra if you have an air conditioner - we've only run into this once.
Most campgrounds that I've seen where you stay for the whole season (long-term, or "seasonal") will have electric meters at your site and you pay separately for electricity (or extra use is added to your regular bill).
It varies on how long you are planning on staying and the campground. Most campground websites will make their billing policy clear, or you can just call them and ask.