$50 Optus prepaid starter kit on special this week for $20
FYI for those wondering here are some of the useful things you can do with this..
55GB data + calls/texts to AU and some overseas destinations - valid for 28 days
15GB data + calls/texts to AU - valid for 42 days
100mb roaming data in Zone 1 countries
50 minutes calls whilst roaming in Zone 1 countries
4 months Spotify premium - https://www.optus.com.au/shop/mobile/apps/spotify-billing (have successfully tried this on a prepaid service)
$40 dollar sim for $15 delivered here https://www.ozbargain.com.au/node/456765