Cost is only one aspect of campground internet access and often not the important one. If you can't get a signal, or the quality is so poor that you cannot get the bandwidth needed to be practical, it makes little difference whether the service is free or fee. Busy campgrounds too often overload the internet access infrastructure, even direct connects via cellular data. We've been in campgrounds where both the campground wifi and mobile data network are fine at 4 pm but deteriorate to unusable by 7 pm or so, when dozens of campers all fire up their phones, tablets and computers to do their thing. A cell tower only has so much bandwidth available and it typically serves a broad area if outside of a city.
