Supercheap Auto is having a Happy Bathurst day sale with many items 50% off or more. Sale starts September 30.
My top 3 suggestions would be the Castrol Edge 5w-30/40 5L for $39.98, Garage Creeper for $34.97 and the Castrol Magnatec 10w-40 5L for $24.99. I've listed the top 23 items as determined by discount (excluding a couple):
If you haven't already, you should join the Supercheap Auto Club Plus. You pay $5 and they give you $10 to spend, so $5 off essentially.