I've tried the 12/18 and 24V: i would highly recommend the 24V one. They also offer 2 years replacement warranty.
Cheapest prices:
24V - Comes in 2 Colors
http://www.harveynorman.com.au/rowenta-air-force-24v-stick-v…
http://www.harveynorman.com.au/rowenta-air-force-24v-stick-v…
The 18V you can get it from David Jones for $129
http://shop.davidjones.com.au/djs/en/SearchDisplay?storeId=1…
12V you can get it for $79 at Myer:
http://www.myer.com.au/shop/mystore/airforce-12v-stick-vacuu…
bough it week ago. it works very good. but….. is it still stock avaliable? when i bought it, i did call lots of stores to check the stock avalialibity. not easy to get in this price