A major cost of any getaway is your airfare.
It's worth looking around as the costs vary widely. It's cheaper to fly overseas in the "shoulder" and "low" seasons, rather than the popular "high" season. For the northern hemisphere, the high season is late Spring and Summer - May to August. It's cheaper on less popular airlines.
Within Australia it's cheaper to fly at unpopular times (very early morning, middle of the day, or late evening). It's also cheaper to buy a ticket that can't be exchanged - if you want the flexibility of changing your time of flight, you need to buy a more expensive ticket.
Estimates - Flying within Australia (non-flexible fare)