Was looking into an cheap way to get Optus Sport and renew my phone plan at the same time so came upon the following:
Optus $180 Sim Starter Kit for $150, which includes 100GB data, unlimited standard talk and SMS over 365 days. Works out to be $12.50 per month.
Add-on Optus Sport for $5 per 28 days (https://www.ozbargain.com.au/node/510843) which works out to be about $17.93 per month. Note there is a risk that Optus Sport may increase it's $5 p.m. rate for prepaid customers in future, and you can only lock in the $5 add-on for 3 months in advance.
From my memory I bought it for $120