hey cameron,
I cant wait to have a pond made up for some natives... you lucky bugger! You should definitely get a Tandanus tandanus , I have one in with my americans, they grow fast, are peaceful and active (more at night) and definitely develop a bit of character. I'd love to have a Murry cod too... they get bloody huge though!
Good luck Cameron, oh yeah there's the Crayhaven Fish Hatchery near Karuah which has natives of all types, I'm not sure of there web address but if you want give em a bell and see what they reckon you should get... they'd be a bit cheaper too even though, like you said, $6 aint much for a fish hey.
see ya mate.