Depending on how much the purchase price is in japan (which depends on the condition of the car, mods etc), and also where its bought from it can cost between $9000 to $13,000 landed and complied ready to be registered.
Here's an example of the price breakdown:
Car cost (in Japanese YEN) ¥280,000
Agent's fee in Japan (FOB charges) ¥100,000
Exchange rate (yen to AU$) 96.00
Total car cost in Japan - $3,958
LOCAL COSTS
Import Agency fee $1,000
Shipping ($2,045 from some Japanese ports) $1,850
Import Duty (10% of FOB cost) $396
G.S.T. (10% of CIF value) $545
Cost of compliance $2,200
Total cost before registration (AU$) $9,949
So you can see a car that costs about $4000 to buy in japan will cost about $10000 all up, ready to register in australia.
Use this calculator as a guide:
http://www.j-spec.com.au/calculator.xls