Migrant where are you in Perth? We arrived here before Xmas but have lived here before and DH is a Perth boy.
I think it is worth reiterating that Australia always was expensive, it's just that the exchange rate made it seem cheap. Remember that you will be getting paid in Aussie dollars and if you stop converting all the time it is much less daunting. The days where you could sell your house in the UK and use the exchange rate in your favour to buy a mansion are long gone but exchange rates fluctuate and this will not always be the case. Also when you go on holidays home the buying power is great!
It is also worth pointing out that you pay for public (state) school in NSW on a 457 but not here in Perth.
Everyone's experience is different but I have a nurse friend in Oxford (where we lived till earlier this year) who would pack up and go in a flash because as a senior ITU nurse she would make 2-3 times what she makes in the UK and can have more flexible working hours, or so she tells me. They are looking for a job for her DH now.
ALso I think a lot depends, as others have said, on where you were living in the UK. Housing in Perth is very expensive but so was housing in Oxford. A 4 bedroom house here is about twice the total size of a 4 bed house in SE England cities.
Schooling also varies from area to area. We've moved from a situation where for a variety of reasons we would have felt compelled to send our DCs private in Oxford from reception to one where if they go private it will be in secondary school, and we will be two minutes walk from the local primary.
We rent a fully furnished (very strangely so, but ok for now, and glad we're not staying much longer) 3 bed townhouse in Cottesloe for $700/week so if you look around you can find great deals. (bear in mind that furnished here is very unusual and so more expensive) The problem with securing rentals in Perth is that it is so competitive it is best to do it when you get here and you don't always get a clear picture from overseas.