SA historic plates cost a whole lot more. You can pay any amount they choose to charge you. I think they charge higher for plates with numerical patterns.....
http://www.transport.sa.gov.au/fees/number_plates.asp
As for Transport SA being picky about the people who buy the plates...... how many asian do you see with the plates on their Mercs and Hondas??? Quite a few. I doubt Transport SA really cares about WHO buys the plates, as long as the person has a fat enough wallet.
If you want to have a plate that looks similar, but costs less, get a personalised plate (white writing on dark blue background) and choose a plate that begins with "OOO-...." , then go and get some matching plates made in a colour closer to black....