If the order is under AU$1000 you don't have to pay import duty and GST. The $1000 includes handling charges, but not shipping. If it's over, the normal rate is 10% GST and 15% Customs Tax on top of that. Also it needs to be a private purchase to not be taxed, items bought by business are automatically taxed.
If you know you have to pay the tax/GST, speak to a customs broker beforehand. When you pay, Customs makes you fill out gay forms for every part you bring in, and specify what category the part fits into. But it's not that easy, there's around 250 categories for automotive gaskets alone. The broker charges around $100 and makes life so much easier.
True it sucks about having to pay extra, but price all the same shit up locally you'll still come out miles in front
