Mate, while you don't have kids HKG is very affordable. I joined CX a long time ago and watched many of my peers leave(B scale) to join QF/EK etc. I think I can objectively say that CX is the best option going for us antipodeans. I don't mean to suggest it is a benevolent benefactor but it is vastly superior to QF, ANZ EK as current options.
Depends what you want out of your personal and professional lives. What I do like about CX is that it is possible to get basings etc...I believe NZ base is full at the moment but dead man's shoes means that with our expansion there should be many FO slots soon.
Back to your original question....my cost of living in HKG(wife, no kids) was half what it was in Oz with a kid...cost of living in HKG with kids is mega expensive. Just remember there is nothing stopping you joining for a while and choosing to leave later...