Repco have got some great prices on oil in their latest catalogue The ones that stand out the most are:
Penrite Everyday Plus 10W-40 Semi-Synthetic 5L - $22.99
Castrol Edge Titanium 5W-40 5L with free oil filter - $44.99
Valvoline XLD Premium 15W-40 4L - $12.99
Castrol GTX 20W-50 5L with free oil filter - $14.99
As a side note, the Castrol edge 5w-30 variant was recently $34.99 as posted here which is a great price and hard to beat but the 5w-40 is still a great price at $44.99 with oil filter.
The specials start on 3rd October until 13th October
Penrite doesn't contain friction modifiers so they rate it for use in motorcycles with both wet and dry clutches. It's much cheaper than motorcycle specific oil which is a bit of a scam.