Just make sure you research and follow the BLM regs on dispersed camping (they have exclusions on some of the more well traveled roads) - and know the administration of the place you happen to wind up ... I've heard rumors that they're actually enforcing the camping regs and issuing citations to violators this week, during EJS. Now, GONE isn't nearly as big as EJS, so there may be a bit more leeway; but we don't want to give BLM or anyone else any reason to poke at access any more than they have ... not that you guys would, I know I'm preaching to the choir, just wanting to give the heads-up.
If you're not too worried about the comfort level, I've had several recommendations to try Area BFE for unimproved camping ... might be worth checking with them for availability, since they're private and administer their own land.
I think all Nissan folk should hit GONE at least once, just be prepared to experience the trails in larger groups than you might otherwise be used to ... it's a great event and the camaraderie can't be beat. For lodging, the other option is a condo at either Rim Village or Rim Vista ... VRBO administers a bunch of them, and there are other places to book as well ... if you can find a way to split it amongst a group, they can actually work out to be quite reasonable on a per person per night basis. Plus they have the added benefit of being the place where a large number of attendees stay, so there's always informal night-time/evening goings on (and help wrenching, if it becomes necessary).