It is all about land values. It might be as low as $200-400 a month in the rural south or southwest, even lower during the summer in southern snowbird colonies. It can be $2000-4000 a month anywhere close to a major metropolitan area, i.e. about the cost of a tiny studio apartment in a scruffy neighborhood.
Season comes into this as well. Along the mid-Atlantic coast, in resort parks on or near the beach, winter rates might be $500 a month for sites that are $500 a week in peak season. South Florida, this reverses, the high is winter, the off-season is summer.