Looking for good deal on oil for car is getting harder.. we are largely at hands of a duopoly of Repco & Supercheap

I normally try and get a 20L can, to allow me to service our 2 cars over a year or two.. 

I previously have purchased 20L for 150-200, but the oil I normally get is now 330.

You think there would be a good discount for 20L vs 5L, but the difference is not significant.. and the "eco" cardboard packs are sometimes more expensive than plastic containers..

I think commerce commission should look at these companies.. as well