I backpacked Brisbane, Sydney and Melbourne for close to a month last December. Visited the outskirts and Gold Coast too. Spent most of the time, say 2 close to 2 weeks in Melbourne.
Food is generally expensive, a plate of fried rice in a food court in Chinatown, Melbourne is easily 8 dollars. Transport is expensive too, from crown casino to my residence at Box Hill in a cab for 15 - 20 mins costed me 60 AUD. (Those electric trams are a better idea, or if you got a Singapore driving license - Rent a car then. Their driving culture is almost similar as Singapore.. the traffic's better too)
I'd recommend going to Philip Island for the magnificient view and to see lotsa penguins. Weather is pretty cold, it was summer when I visited but still cold and bitter especially at night. Melbourne is slightly colder than Brisbane and Sydney.
It was a wonderful experience, save for some unpleasant incident - Chinese bashing is common especially in Gold Coast and Sydney. But people are generally very nice and warm.
Remember to pay the shopping malls and surf shops a visit, their surf products although almost the same price as Singapore, they got a larger variety of designs you can't find in SG. Even I, an anti-surf wear guy... Got tempted and bought afew surf shorts and even ripcurl jacket

It's a grand idea to explore the wild life parks, theme parks and other attractions. But don't forget to shop! You will find a lot of nice things there.
For Hotels, just go to some 3 star hotels - they're fine enough, unless you're on a huge budget. I can't remember the names of the hotels I stayed in; I'm quite a frequent traveler. When I was in Melbourne though, I spent the last week renting a holiday bungalow in Box hill, costed me close to 300 a day. But it was worth every cent.
'Nuff said, just go and feel the Aussie experience. While, I get ready to wander Hawaii this September
