Hey mate. I am Aussie and there are a few shops that are not so well know but much cheaper and can be trusted as I know people who get their parts from there and I also plan to.
Shops:
MSY
Umart
Those are the two shops that sell cheap parts but not extremely cheaper but cheaper than the parts sold at popular computer store. However if you do go to these store, you must first be prepared to know what to buy.
But instead if using PCCaseGear, try PCPartPicker which you may find a cheaper part and will inform you wit any incompatibilities.