Try adding yourself to regional lists in your own state and neighboring states; you might find like-minded ridesharing types. http://regionals.burningman.com/na_index.html
There will be a rideshare board on the Burning Man website in June or July.
Two years running, a friend of mine & I rented a cargo van and split the costs. Not cheap, but we were able to fit a monkey hut, two bikes, a shower structure and evap pond lumber in there, plus all the usual stuff. We could have fit a third person's items in there (but not a third person, no third seat) if necessary.