There are four really cheap phones in the current Kmart catalogue. Some of them offer basic calls and text features and are only good as backup phone just in case you need one for your car or at home.
Check their prices:
Vodafone 541 Prepaid Mobile - $25
Unlocked Samsung E1170T - $29
Telstra Smart T3020 Prepaid - $99
Optus Nokia E71 Prepaid - $199