Woolworths has 50% off the prepaid simcards at the moment. If you buy through the website, it comes with free postage and is eligible for cashback.
Both Cashrewards and Shopback currently have $20 cashback for the $40 sim, making it essentially free if you're successful.
*Note that cashback requires activation within 30 days to be accepted.
Thanks Op! got one - hope the cashback comes through!