I don't know how many are available, but larger camps can rent large greywater tanks from the same company that does the portajohns. We did one last year, and it only came out to 10 or 20 bucks per person in a camp of 15-20 (can't remember exact numbers, but the camp I was with last year is doing the same thing again this year.. They drop the tank off, you dump your water in it, and they haul it off at the end of the week. The tanks had a tight double lid (small inside big, for small or big jobs) and it was WONDERFUL. Smaller camps can handle greywater pools and such, but for larger camps, this is a great alternative, and makes sure nothing hits the playa.
I don't know prices, I don't know who to contact, so on that note, this post is crap, but it's here for those who want it.
OMG, only a week more for all you folks going home. Aren't you freaking excited?