Other AUS guys have tried but it seems between the import duties and cost of freight there really isn't much of a difference considering all the pain and agony you go through.
If you are talking new bikes, $12,000 AUD is about $11,000 USD today. New Warriors sell for about $10k USD if the dealer is in a bind, or $13k list when the dealer is doing good. You are probably better off buying there.
If you are talking used bikes, then you should get a couple of freight quotes first, then add import duties, then consider how much you have left in your cash budget to actually buy the used bike. The money doesn't seem to work out very often.