Make sure they are quoting you on everything like internal fright USA , all custom chargers in the USA , packing USA , unpacking aust , gst aust , shipping itself , quarantine aust , insurance , luxury tax because of the value on your mustang , etc etc . I don’t know the current prices at all . Also ask them about a time frame all up and where will your car be stored until it’s going to be shipped . Where is it going to be shipped too ,which port in Australia and which port is it being shipped from in the USA ? ,the west coast is much safer than the east coast of the US to ship from .