Use the NW entrance! 2wd acceptable
Free! Easy enough to find if you use the coordinates given by the Dyrt. I only saw maybe 6 official spaces to camp, but there's probably more that I just couldn't access with 2wd. I took the Northwest entrance initially and had no problem getting to the campsite. Just a few bumps. Using the other entrance, I found too many bumps for my minivan to get over.