If you're keen on getting an iPhone XR for the cheapest price possible, the best way to go about it currently is to go with one of the $79 per month plans with Optus (which gives unlimited calls, no international, and 100GB data) for 24 months. If you buy the plan through Harvey Norman you will be eligible for a $200 eftpos card (which effectively brings the plan down to $70.6 per month).
Awesome deal. I just picked one up. Make sure the Harvey Norman you visit can supply to $200 eftpos card (I have spoken to an online Optus rep who said they wouldn't be able to do it although once in store Harvey Norman was more than happy.