Nuts! Ya, that is Google's choice not mine. Once they start supporting Australia the plugin will work just fine for you. In my defense, I do mention on the download page feature list this:
* Set your preferred currency code, includes both Google supported currencies, USD & GBP.
I suppose it could be more transparent. Anyway, if you email me your transaction id, I can refund your purchase, or if you prefer, I can give you a partial refund of $5 USD and email you the Nice PayPal Button plugin.
Let me know what you would like to do. And sorry for the inconvenience.
~ Best regards