It's not just import tariff (which is 10%), the main tax is the bloody luxury car tax (25% of wholesale price). Most expensive cars have nearly half their on-road price made of taxes (GST, import tariff, LCT. stamp duty). Add to that the lower demand world wide for RHD cars, and our smaller, isolated market compared to the US or Europe, and the you see why those cars cost so much more here. It could be worse - check out the price in NZ or Singapore
Yes it is a rip off, but you just have to accept that in AU "they" (the government) don't care about people who might want to buy/drive flash cars. If you buy a cheap car (Korean/Japanese) or a locally made car (Ford/Holden) you get more value for money relative to other countries like the US/UK. Over $50k you get reamed - not sure it will ever change in this country.
Actually when I lived in the US, the ONLY reason I could think of to stay was being able to get great cars at half the price as in AU, but nearly everything else about living there sucked, so here I am
PS: Remember also the exchange rates fluctuate - when you only bought US 50c for AU $1 the difference didn't seem as large!
PPS: Markets are also funny things - the fact that flash cars cost more here also means that we have a much more active used car market, so you get much better resale value (less depreciatino) than you do in the US - so that needs to be factored in as well.
Cheers,
Beej