Klamath Falls is directly on the way to Burning Man from Seattle if you take the route I've come to prefer over the years. That place is probably a good option, though you could almost certainly hit craigslist for a garage-sale bike super cheap and give it away after the event.
"Whaoomph! Whaomph! Burbbleburbblepattpattpattpatt... WHAAAAAaaoooaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa........!!!"
Top fuel dragster, by Elliot Naess