In the UK, I'd budget for £10,000 a year and have £20,000 in your back pocket for unforseen, uninsurable happenings, such as needing a new engine. The is for 50 hours a year and trues out at £200 per hour. This is more expensive than renting, but gives you greater freedom to do what you want, when you want. Some people 'get away with' a smaller figure, but don't budget for it.
I'm sure the Australian figures aren't markedly different. Don't know what the current exchange rate is...
TOO