Yeah things do cost more here in Aus, but not everything, for instance alcohol is super expensive, like $40 a case. And fast food isnt cheap, BUT if you know where to shop and can make a meal or 2 for yourself you can certainly save money earning $500 a week. Working as a liftie (which i have no experience as) im sure has its perks and pittfalls, but i wouldnt just go and work in NZ cos the snow is better. Queenstown NZ (coronet peak and remarks) is just as expensive as AUS if not more so in some instances. Is the snow better, yes, are there more terrain options, yes. But i would figure working as a liftie you would have limited time to really ride anyway wouldnt you? Anyway my suggestion if you were keen on Aus would be Perisher, Thredbo or Falls Creek. I wouldnt waste my time with Mt Buller. Mt Hotham can be awesome (does get powder and has some nice terrain options and tree runs) but can be hit or miss.
Im bias cos i live in Aus but do some research and then decide where you want to go, I would be guessing either option would be similar, but you may end up saving a bit more money in Aus. JMO
my names's Petey and i have gigantic balls