Chode,
You're looking at a serious wedge of cash whatever you do.
You'll need an ancestry visa or a European passport for starters. (Note, there is mumblings about the ancestry visa being wound up possibly next year.)
I don't know the pricing of the WAAC.
To convert your Australian CPL to a JAA CPL with IR and ATPL exam credits (aka "frozen ATPL") you'll need to do a JAA medical (if you intend to get a UK JAA CPL then the
initial class 1 medical needs to be done in Gatwick).
Then you'll need to do the 14 exams. You can do them in Perth (WAAC) or distance learning (have a look at Bristol Ground School) or do them full time in the UK. Budget about 2000 GBP plus other such living expenses.
Exams themselves are about 700GBP.
Medical I think is about 250GBP.
License. I can't remember. Budget about 150GBP and a day of your life.....
That's the theory done.
The flying. If you hold an ICAO IR then you need to do a minimum of 15 hours of which some can be done in a synthetic trainer. Budget about 3000GBP at least! Remember to add in some for the CAA examiner. That's another couple hundred pounds.
Now you have a nice shiny blue book CPL/IR with ATPL credits. You now have ~ 7 years to "unfreeze" it.
MCC's a big thing here. Budget another grand or so.
As a few have alluded to the pay for rating thing is alive and well in the UK.
easyJet's TRSS is 23K. Ryanair are still charging for low houred guys but now have dropped their "TRSS" for bonds for experienced jet guys. Actually, easyJet's done the same for experienced jet guys.
Air Southwest don't charge for a rating but they don't pay the best. 18K for an FO. It goes up to 21.5K for an FO with an ATPL. BACon don't charge for a rating, they fly Dash 8s and regional jets.
There is hope but it's a risk. There is signs of a slow down on the long haul sector but the European short haul stuff is still booming.
Be aware of the typical cyclical nature of this industry. 7-10 years.
For factual info, check out the UK CAA's LASORS online.