Not too sure actually. Might be cheaper to film here than in the states? And easier to get a permit? I'm sure Mr. Brumby and friends wouldn't say no to having a hollywood film being shot in Melb if it meant more $$$ being brought in. I guess I could ask if they intend to film more scenes in Melb...
My GF is with an agency, she specifically got called in as an extra and yeah they get paid. She's earns a pretty good amount, surprisinly. Gets paid by the hour for however long she's on set for, plus catering etc etc. She could stay on set for 15 hours and only film 1 hours worth and still get paid 15 hours. So it's not bad at all...she actually wanted to sign me up also...might be fun!
(I'm not sure if i'm allowed to be saying this, so i might get in trouble but oh well...but she just got called in to cast for some new australian medical drama to play as one of the female doctors girlfriends! She rides in on a motorcycle apparently, talks a few lines, then makes out with her before they say goodbye! hahaha!! how cool!)
As for other extras, they might have extras that are happy to do it for free and just be in the movie for the hell of it...but im not entirely sure...