(1) Container: Freight forwarders will send cargo by sea by container at rates far far far below those being quoted. Rates are usually by the cubic meter and weight is usually irrelevant as long as you are not shipping pig iron or similarly dense material. There may be a 1 cubic metre minimum size. Pack it all in :-).
You will have to get somebody who will arrange to incorporate your "tiny" load into a container full and pay extra accordingly. I do not know rates from USA to OZ but eg from China to NZ is about $US80 per cubic metre !!!! and delivery times are in the 4 to 6 weeks range. Even after paying freight forwarder and customs agent charges at the receiving end you should be comfortabley ahead of the other alternatives suggested so far.
(2) JUMBO boxes: Companies like DHL offer "Jumbo" boxes or similar with a 25 kg weight limit and fixed size. This may be useful. They are not cheap compared to container freight but otherwise are about as cheap as you can get for airfreight.
(3) Buy it there: What are you taking that is not already sold in Australia?
Consider buying or hiring. Second hand buying (look at ebay) may help. You may be able to get somebody in Oz to buy for you in advance. If you have no contacts there I have some friends who MAY be willing to assist for a reasonable fee.
(4) Prebooked bag - new service: Air NZ has as of November 2012 introduced a pre-booked bag service and this may be being copied by others. This allows you to book in excess baggage (check in with the rest , just pre book) at far less per kg than normal excess baggage rates. Hong kong-Auckland cost me about $US70/23 kg for a first bag ans about 50% more for a second.
(5) Bilge class:
OTW far far shot department: Talk to some yachtsmen - somebody may be willing to carry your well sealed gear bilge class :-). They may want signed in blood indemnity re contents. Same may apply to freighters. Choose well :-).