Money & Costs
In recent years the Australian dollar has been holding its own against major international currencies like the greenback and the euro, so the country is a less economical destination than it used to be in the days when the Aussie dollar was financially malnourished. That said, while manufactured goods tend to be relatively expensive, daily living costs such as food and accommodation are still fairly inexpensive. The biggest cost in any trip to Australia will be transport, simply because it's such an expansive country.
How much you should budget for depends on what kind of traveller you are and how you'll be occupying yourself. If you regard sightseeing and having a good time as integral parts of the travel experience, prefer to stay in at least midrange accommodation, and have a stomach for regular restaurant visits, then $90 to $110 per day (per person travelling as a couple) should do it. Travellers with a demanding brood in tow will find there are many ways to keep kids inexpensively satisfied, including beach and park visits, camping grounds and motels with pools and games rooms, kids' menus and youth/family concessions for attractions.
At the low-cost end of travel, if you camp or stay in hostels, cook your own meals, restrain your urge for entertainment and touristy attractions, and move around by bus (or in your own vehicle), you could probably eke out an existence on $50 per day; for a budget that realistically enables you to have a good time, raise the stakes to $65 per day.