Fred, that's a big topic. You might join the Good Sam Club and get their magazine and do some reading there. Visit some campgrounds, get one of the campground directories, like Woodall's, or the Good Sam directory that lists a lot of the prices. You'll find that prices vary tremendously with different parts of the country, amenities provided, facility layout, placement and quality of utility hookups, sometimes the time of year, etc., etc. Are your roads and campsites going to be paved, gravel, or dirt? "Pull through" sites are much more popular than sites that require backing in. Are you planning a "destination" park or are you on a major thoroughfare and will cater to just overnighters? What kind of water pressure will you have? Some parks have signs warning that a pressure regulator is necessary because of the high pressure while others may have minimal pressure? What kind of sewer system? Septic type systems sometimes have problems from chemicals RVers put in their holding tanks. What electrical system will you provide. Many "old" parks only had 15 amp service, then most went to 30 amp service, and now 50 amp service is popular. Will you provide cable TV? Is telephone service available? Showers, restrooms, laundry facilities, swimming pool, LPG, store, recreation facilities? There's no end to what you can do, if you have enough money.
As for rental rates, I think we've stayed at one time or another in everything from the very best to the very worst, and from cheap to "you gotta be kiddin'". As with any real estate deal, location is the key factor. In my area, just north of Dallas, rates right now in decent parks are $330 to $350 a month plus electric or $20-25 a day, while my brothers are in a much nicer place just north of Waco for $150 a month plus electric or $15 a day. And 11 years ago, in Virginia, we worked one summer at a park that charged $30 a day or $600 a month. Daily rates usually include all utilities, although some parks add a dollar or two a day if you have an air-conditioner, while monthly rates usually do not include the electric bill (you have a separate meter).
I don't know where you are, but those are just a few thoughts off the top of my head. Good luck with your endeavors.