would you be shipping from the east coast or the west coast? Or is your car somewhere in between and must be truck shipped to the coast. Here are some ball park figures: Car is in Arizona. Shipped to California port ($500). Loaded on boat and shipped shared container to Oz ($1000). Off-loading in Oz and customs clearance ($500). Duty on cars over 30 years is 10% of the value of the car (probably purchase price), including the shipping costs. Duty on cars under 30 years old is figured as the value of the car, plus import duty of 15%, plus freight, plus 10% GST. (Note, all figures in US currency, not Australian dollary-doos).
Oh yeh, I just read jerry S's reply, and you won't pay import duty, just GST. Import duty I believe is for cars under 15 years, something like that.
EDIT: I just re-read jerry's reply, and see said what I was thinking. Although, I don't think there is a duty on old cars, just GST. I think if you import a newer car, under that 30 or 15 or whatever year limit you pay the import tax, but not GST, but if it is older, no import, but GST.