Like the guy above I have done part of it through northen Arizona and Kingman (home ot the oldest Harley Davidson shop in America, so I assume the world)
Was fantastic and aim to do it myself (on a bike) one day in the not to distant future from east to west
If you are going to do it (and I have no idea on costs) you may want to consider contacting the American Embassy for advice, as a friend of mine did and was surprised by some of the advice given (positive and negative)
Apparently, there are parts of the road that (in reality) don't exist like it was many years ago and also one or two very 'dodgy' areas to pass through
But I think like on all trips you need to keep your head and this must surely rank as a 'once in a lifetime' achievement
Let us know how you get on