I'm currently in Brisbane too. Z4s are really pricey here compared with the UK. If you are coming to stay for good, take my advice and bring your car with you!
I live in Townsville, QLD about 2000km north of Brisbane and z4's are vary rare around here.
Chrisman85 - I have a 03 3.0i and paid around 40,000 aud lots more expensive then UK but also BMW is much more exclusive here, being the euro import. Look at www.carsales.com.au for a good indication of available cars. (only 1 //M for sale in the country )