Your biggest cost will be rent or mortgage. Back in 2001, I was paying $2200 per month for a nice 3 bedroom house in Greenwich. I can only imagine it would be more now.
In my experience of living in Sydney from 1998 til 2001 in Greenwich, and out of a suitcase from then on, Sydney's grocery and petrol prices are about the same as Melbourne's.
A comfortable salary in the Sydney area would be about $100k for a family, a little less for a single person who has simple tastes in cars (or who can do without one). I wouldn't want to live in Sydney on anything less than $60k - but many do and I feel sorry for them.
Andrew