Yumas can be expensive in the states, but not as expensive as you're describing.
It sounds to me that Australia could really benefit from aquaculturing florida rics. You're saying that they are available, just really expensive. Typically florida rics reproduce pretty well, albeit a little slow, but definitely culturable by hobbyists. It might take a small investment, but I would buy a couple of expensive florida rics, and just start culturing them, fragging them, and either sell them or trade.