If you have the tools and skills to fabricate parts and brackets, it can be done for maybe 300-400 USD. But since you're asking, I'm assuming you don't. In that case, you're probably better off buying a conversion kit and paying someone to install it. In that case, I would guess somewhere closer to 1000 USD.
I'm not sure who to recommend in Australia, but I know that there are plenty of Land Cruiser-specific clubs there that can provide specific information.
I would try asking at
http://www.outerlimits4x4.com/
Good luck.