Family of four - about $24,000/yr with no lifestyle changes (go out to eat multiple times a week, at least one 2hr round-trip per week to nearest large city to do shopping, one large vacation such as 3-4 days of Disney plus a 7day cruise). $18,000 would see a reduction in how much we go out to eat (multiple times a month vs per week), would try to bulk-up more on our shopping trips to reduce them to 2-3 times a month, and the vacation would be a bit scaled down (just some Disney, or cruise, perhaps 3day cruise and 3 days Disney?). $12,000 would have us virtually never going out to eat, we'd definitely need a deep freezer to reduce our grocery trips, staycation (hate that word) consisting of us camping at a nearby park perhaps?
All those numbers are based on us living in Tennessee. Haven't run the numbers here in Australia, I don't think they'd be that far off (grocery spending is similar, utilities aren't that far off, vacations cost more though).