Me and 2 other friends did it in 3 months down the west coast from November 2007 - januarie 2008.
It worked out at about a 1000 pounds a month,camping and sleeping in cheapish accomodation. We did not have any problems with the bikes along the way so no parts was couriered. Think the most expensive item is fuel for the bike and after that most probably accomodation. We also met up with ed,dan and chris along the way.
Hope it helps a bit.
How are you ed,things going all right there in the UK? 
Cheers
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