I can assure you it won't go mail..
http://www.shippingmasters.com/
Try something like that, there are other ones cheaper, but that'll get you started...I shipped a quad in a steel crate from Michigan to Oregon for $450.
I shipped a quad from Florida to Michigan on R&L trucking (semi truck, straight pallet style) for like $200 my cost, but I got a deal..
For a dirtbike the best way to do it cheap would be a trucking company, such as R&L, Roadway, etc...just drain gas and secure it well and they won't care.