We stay at a lot of KOA's across the country when traveling. They certainly have different levels of quality which usually depends on the age of the park. Generally, we have found KOA's to be reasonably priced $35-$45 for a pull-through site.
Recently we stayed in one of the most expensive KOA's that we have ever been to (twice). It's in Billings, MT, on the Yellowstone River. It is run by a family who have owned it for 30 yrs. or so. There are two big family homes at the entrance to the park and the park is immaculate! If I recall, it was $60+ a night for a pull-through site and the park was packed. It's only open April-October and I have found parks like this in destination area's usually run more. Their stated base rate is $47 a night.
MM.