Coinspot is your friend. They are pedantic and annoying to set up with ID, etc. but once you get set up, you can transfer (a minimum of ) $50 via the post office's POLI account (if your bank account has one) and then buy Steem that way.
What is annoying is having to convert Steem to Etherium in order to get money back into your bank account.
You also have to declare any profits to the tax department as income.
Alternatively, what you can do is find a Steemit meet up in your local area (Adelaide has the best one so far) and find people willing to sell you Steem for cash.