We just stayed at Gouldings RV Park in October in our 38' coach and had no issues with the staff. In fact, they were very helpful. Our site was level and the hookups all worked great. The sites are dirt, so if it's rainy, be prepared for mud. The location is spectacular, and in my opinion, worth the price. We were located in the upper row (site 40), which is where they seem to put most of the big rigs, and the view was awesome. There is a dry camping area within the Tribal Park, but this is just parking on gravel with a picnic table for about the same price.
I recommend taking one of the jeep tours. Even though you can drive your Toad on the "Improved Dirt" road to John Ford's Point, the Deluxe Tour gets you into areas of the park that are not accessible on your own. Our guide was extremely knowledgeable about the park, it's history, and the Native American Culture. Tours depart from the RV Park and you can also book them right in the park office.
Hope you enjoy Monument Valley as much as we did.
Safe travels!