Actual expenses we have in Brisbane (2 DCs, one in daycare, one in state school prep).
Rent: $440 per week. 3 bed house in nice area, 25 minutes from CBD.
Car: $480 per month - Mazda 6 estate bought new on finance. Rego (car tax) includes 3rd party insurance, and costs $660 a year.
Food: $150 per week - don't do all your shopping in Coles/Woolworths, use the local shops instead - much cheaper and better quality.
Electric: $350 per quarter - no pool, use air-con a bit, but not much.
Water: $25 per quarter
Foxtel: $85 per month
Phone line: $15 per month
Internet: $35 per month
Health Insurance: No health insurance - had no problems with Medicare for myself (hip problems needed MRI and consultant) and DS (annual trips to see a paed). As private medical cover is a rebate system rather than insurance, I see it as a total waste of money. Having said that, ambulance cover is free in Qld.
Contents Insurance: $300 a year
Daycare: $90 per day (once we've become permanent residents, this will be rebated at 50%)
Train: $150 per month
Petrol: $140 per month
Mobile phone: $15 a month
School fees (state school): $180
Before/After school and vacation care: $22 a day (price includes two after school activities per week which change each term, including dance, martial arts, soccer etc)
Additional school fees: $0 per year
Activities (swimming/gymnastics): $150 per term per child (not through school)
Return flight to UK for 1 adult and 2 children: We go on holiday in Oz instead.
Now, obviously we don't have the lifestyle that many of the posters above have, but we hardly live in abject poverty. We have annual passes to the Gold Coast theme parks ($99 per person) that we use about once a month, the museums and art galleries in Brisbane are free (and very good). We also regularly go to the beach (free) and the local parks are excellent. Both me and DH work, and our combined income is ~$160k before taxes.
The local state school is rated more highly than any Catholic or private school within 5km, and we had no problems enrolling with 6 months notice. DS (who has some problems) has settled in brilliantly, and we've had really positive feedback and results. A full set of uniform for the year set us back about $180.
Also, if you're earning Australian dollars, don't try and convert everything to GBP. The AUD/GBP exchange rate isn't the same as the salary or cost of living comparison. Generally the salary/COL rate is 2.2AUD:1GBP. Also savings rates are much higher over in Oz.
If you want to come over to experience Australia, then I would suggest you don't stay within the British ex-pat cocoon. Australia is a wonderful, amazing place with its own share of ups, downs, ins and outs. I love it here, and I would never move back to the UK unless we were deported.