Very approx $2000 ~ $3000 in a container for shipping only wharf to wharf, plus fees, etc. Have friends who spent $10K to import a pre war car from the USA all up (local transport, steam cleaning, sea freight, duties, and more).
Use an agent:- do not try to your self. A lot of companies do this. Look in any collectable car magazine:- Unique Cars, Aust Classic car and more. If old (30ys plus) not so difficult. If modern can/will have a lot of compliance issues for registration, taxes. fees, GST.
Aust Customs are well aware of the value of cars & all schemes/scams to avoid /evade taxes, GST etc. Google "importing car". There is information on the gov.au web site.