If you're buying a GTR that's already landed in Aust I'd preferably buy one through a car club on Fb or SAU itself. If a member here doesn't wish to fix up problems, he's more likely to sell it through gumtree or carsales.
If you're trying to source it from Japan, your importer will try and procure one from private treaty or at an auction house. Some auction houses attract better or poorer/cheaper cars than others. Some importers may have a man on the ground to do a physical inspection as well as pore over the auction sheet. Some Japanese owners may set too high a reserve and the car may get passed in only to reappear a couple of weeks later.
Doing your maths:- Add about AUD$12,000 to your Yen Bidding Limit and then compare with what you can procure here in Aust.