I agree that on the average KOA's probably are at least $5 higher than other parks in an area, but like most averages, this statement can hide significant variations both up and down. We recently stayed at the KOA in Salt Lake City which is a really nice park literally in the city, minutes from Temple Square. We had a full hookup site for $42 plus tax and that was just a daily rate, not a weekly. Having been in 31 states since January, IMHO this is a very good rate for an "urban" campground near a major city. The fact that it was a really nice place to stay made it an even better buy. In contrast we paid >$60/night in St. Louis for a non-KOA campground with virtually no ambiance but it was was the closest CG to where our son lives. If we didn't stay at that one our choices were literally a "trailer park" at which we refuse to stay or an additional 30 minute drive further from town. For us, for a short stay, it made more sense to pay more for the CG and save time and gas.
When we are looking for a CG in a particular location we try to strike a balance between quality (ratings on RVParkReviews), location, and price. We won't stay at the cheapest place just because it is cheap, but nor will we pay for resort amenities if we are in an area for a brief time and are more interested in sightseeing away from the CG. I don't reject anyplace just because of its brand affiliation (for what it's worth, I dislike Jellystone Parks far more than KOAs), nor do I reject a place just because it's price is higher than the average we try to maintain. I keep fairly accurate financial stats with Quicken and have found that a few nights at a high cost urban CG quickly get balanced out by, for example, a week at a COE site where a full-hookup costs us no more than $12 (with a senior discount pass). Since we are full-timers we can take this perspective because we know that we will, on the average, spend far more time in rural areas where we like to be when the weather is good than we will in urban areas. Usually, but not always, that will translate to lower cost. We spend two weeks with full hookups at Colter Bay in Grand Teton NP this summer; it wasn't cheap, but, in the words of the MasterCard ad, it was priceless.