The cheapest way would probably be to head up north. There is quite an informative thread running here:
http://www.pprune.org/dg-p-general-a...g-top-end.html
Umongst the discussion there is mentioned the operators and towns and places that offer the greatest chances. The basics are to get a NVFR (even if you have a MEIR or CIR) once you get here and arrive up north around January / February. A NZ night VFR to Aus NVFR is a night cross-country and a night cross-country flight test. Ask if the school can do it in-house and you might save the A$400 examiner fee.
Alternatively, alot of kiwis end up converting their instructor rating and instruct at schools. I am not sure of the process involved in converting but their training system seems pretty different so I can assume it would be more complicated (read: costly) than the simple paperwork exercise converting the CPL/MEIR.
Plenty of instructing work to be had, it seems, judging by the steady stream of instructing job adverts on the AFAP website.
Australian Federation of Air Pilots - test page - 2
Good luck.