Well Damoo a 05 V6 is about 14kUS and a GT arround 20kUS , say about $500-700 transport cost to long beach then 3k for slow shared container or 7k for single straight fast container, not sure what customs inspection fees are, 43% taxes,RAWS,Transport to who ever you get to convert, rego inspection, stamp duty , compliance plate and registration. I'm fairly sure you can bring in a second hand Mustang as i know melbourne motorsport do.
I would say somewhere arround 65k-75k on top of the purchase price but as you can see lots of variables. if you are really interested make some enquires to some converters, importers, RTA and compliancing.
Good Luck the S197 is a fantastic model.