As Paul said, some people selling their cars don't really know what they are worth, I have seen an average 2005 coupe up for sale for about $35k less than a year ago (he was clearly dreaming), I have also seen 2003 coupes for well under $20k with around 100,000km on them.
Do your research and you will get an idea of what prices are reasonable.
If you want to import your own, sign up with a reputable importer, they do all the hard work for you.
If I were you, I would be looking at importing a V36 350GT, the prices are quite good at the moment. the 370GT prices are still up there a bit.
As for the car you mentioned, I would expect a white 2003 Manual Premium in reasonably good condition to sell for around the $20k area, assuming it is a private sale and is already registered in Aust.
Maybe a little more if it is in very good condition.