The US pay appx 1$Au per litre we pay appx $2.
You sure about that?
100LL - Aviation Fuel Prices
And Europe, for good measure:
www.TheHangar.co.uk - UK AVGAS Price Data
Also, excise in the US is 19.4 cents per gallon, or 5.1 cents per litre. So whatever is causing our AVGAS to be 25% more expensive, excise ain't it and won't be it any time soon. (The only consolation for the US is that the excise goes direct to the FAA.)