I guess the good thing is that there are never a shortage of Mustangs in America
Only true if you have a decent and realistic budget to start with and deeper pockets.
It's getting very hard to find decent Mustangs at hopeful budget prices because they are so popular over there too, the vast majority of owners are up with the play and know what they have.
And the current US-AUS $ exchange rate has made things tougher this end.
Do your homework on import costs which include import approval, shipping, insurance, local freighting both ends, GST, inspections, customs and quarantine clearances, plus engineering assessment here, repairs/upgrades for local regs, and state registration, and perhaps asbestos removal.
The reality is that this is 2017 not 2007 and just AUS$25K won't get you much of a usable driving car in reasonable condition by the time it's imported, complied and registered, if anything at all. I suggest you hold off and save a bit more.
My 2c worth is that if you don't know your Mustangs then best get local advice and buy local. Take advantage of others' risks and hard work, or you risk buying a polished turd from overseas that once here could cost you many thousands of $$$ to put right. Lots of people even those reasonably car-savvy have fallen into that unfortunate predicament.