TeleChoice's $20 SIM only plan seems like a very good deal - it's $20 for $500 worth of call, 1GB data and unlimited texts. Since they run on Telstra's network, this is a good price for low use plans. You can also include international call into your $500 quota which is a really useful addition.
$20 price is for a 24 month plan but you can get month-on-month for $30.