I was fumbling around the Supercheap Auto website and noticed this particular oil was on clearance for $4/5L. Unfortunately, delivery wasn't available nor were any in stock at my nearest stores.
Thought I'd check the eBay store where I found them still at $4 each - with 38 still available at time of posting.
+$2.50* for additional bottles.
*for my postcode. Might be more for your postcode