It really depends on what your financial commitments are, your lifestyle and where you are looking to rent or buy.
$100k p.a. is well above any measure of an average salary, yet a lot of two income couples earning $250k between them say they struggle.
Generally, living in the more ‘desirable’ suburbs of the major cities (those in the inner rings)-and in particular, in Sydney and Melbourne-will eat up a major portion of your income if you’re renting, but you should be able to find places further out which will still allow you to have a good lifestyle, while still being able to make some savings. Rent, which will be a major consideration, can be $450-$750 per week (average) for a one bedroom apartment on the lower Northern Beaches of Sydney, eg Manly, but then our property market is currently very buoyant.
Eating out can vary from very affordable to very expensive, again it depends on your tastes, and whether you want to change your car every few years, or go on an international holiday each year will impact how quickly your money lasts. If you’re fairly frugal, on $100,000/year, you should be able to live and save, assuming that’s what you want.