I just spent the afternoon in at Customs House and with the Quarrantine Service so i can help shed some light on your questions.

Firstly, the transport cost is determined by
1. Weight
2.Size-cubic volume.
The transport cost is determined by a calculation using both. A seafreight company can only tell you the price.

I just paid $500 USA to have a 200 kg item sent on a heat treated resin pallet from california to Brisbane. The Broker fees at the other end was $200.
The port/arrival fees for my 200 kg item was $400 aussie.
The customs cost was $250 aussie based on the purchase and shipping price combined, plus I then had to pay about $50 to have the Quarrantine service decide whether they would physically inspect the item or not. They decided not.
If they had of decided to do the full inspection, It would have cost me another $400 plus dollars.

I also note, that this paticular item was duties free. That can cost you another $300 to $400 based on a $2200 aussie purchase/shipping total.

Also, I did all the paperwork and leg work myself at this end and did not use a broker and i got the item customs cleared myself. If I had of used a broker, it would have cost m,e another $400.

If you want good info on anything to do with importing, you must go to the following customs website.   www.customs.gov.au

To see if and how much the duties payable are, go to the same website and look at the import/export drop down box.
then go to customs tarrif, then go to working tarrifs, then go to schedule 3, then go to classifications.
The phone number for Customs Australia wide is 1300 558 099.

I have a checklist of every document you will need to bring in any item from overseas and i can help with advice on how to do it the easiest way. PM me.

Also, brokers are out to rip u off at every turn, so I got professional advice from Customs and it all went very well.
Good luck. Its a minefield.