Mudoch,
I have used the AFT self study books when I was doing my ATPL. They cover everything you need to know. I thought the ATPL coversion was just a Air Law exam, so therefore you would only need the Air Law books and the relevent CASA documents, which would probably add up to $600.
For the IREX you will need all the Jepp's/All the ERC low charts/PCA/ERSA/CAO'S/AIP and a study book. Bob Tait's is popular. I used the Aviation theory centre book and passed it on the second attempt. The Irex is a pig of an exam!
Chopperline on the Sunshine coast is a good school for any flying component you may need to do. I only say Chopperline because they are one of the few schools that are part of a bigger aviation company and therefore may have work available when your conversion is complete.
Good luck in Australia