It cost me $6000 in 2006 to do Maui - Molokai and Keanae - Kahului (via Maliko) races. That did not include Molokai to Oahu, which would have cost and extra $2k at least, so the $10k ain't far off what you will spend. At least the Aussie $ is in your favor, it was $.68 in 2006.

Tip, don't skimp on the support boat cost, pay for a good one that has done the race many times and don't take bananas on board, Hawaiians believe brings bad luck.
Cheers Rambo