Both Aldi and TPG have comparable plans at the moment: $20 for a month including 1.5G of data.
Although TPG has half price for first six months, but from comments it seems they charge more for SIM as well as prepay credit and porting out fee.
Grateful for comments about which one I should get. Live in Canberra. I currently have $20 Virgin Mobile plan with 1.2G data.
Jeenee Mobile - 1.8gb 200 mins Ulimited text for $18 a month.