If you plan to use the program to travel around the country to gain a true cultural experience, you would be better off staying in hostels. If you plan to stay in one location, then renting a shared flat (apartment) would be more cost effective.
Costs in Australia
Shared accommodation will cost approximately AU$130-AU$190 per week and you will generally need to pay a bond of 2 weeks rent plus the first 2 weeks rent in advance. On average your weekly expenses will be about AU$245 per week.