I would agree that bubbas don't cost much especiall if b/f and using cloth nappies.
We use huggies so that costs about $30-40 a box and sometimes lasts a fortnight depending.
Also, not that you would want to rely on this but depending on your financial situation you also get government assistance that is paid fortnightly. You can check out the family assist website and they have a calculator on there that works out how much you would get....