If your like me and procrasanated to long, or for any reason Missed out on the on-site camping this may be the best bet for you as well. Lake Cahuilla still has about 30-40 "primitive campsites" left. so no water or power hook ups. They have showers and a pool. a lake thats for looking at, but not swimming. It seems to be by far the closest camping other than at polo fields. about a 5 min drive. I just got on it and got a spot reserved and thought I would share this information.
1-800-2347275 ( I was on hold for 2 hrs. hope you have better luck)
the site cost 52$ for the whole weekend.
number 12 represents the campsite on this map.
the red x being polo fields.
Hope this helps people in the same boat as me it may be second best but there are deffinatly worse options.
Goodluck! see you there.