The decent Brita on-tap water filter is on sale at Coles, as part of their 20% off Brita catalogue offer. According to Pricehipster, this is about as cheap as it gets, and doesn't go on sale often.
(http://shop.coles.com.au/online/national/brita-filter-faucet…)
Price match at Bunnings to get it for $40 (https://www.bunnings.com.au/brita-on-tap-water-filter-system…).
Edit: The coles website shows the incorrect product photo. This is the whole on-tap system, not replacement cartridges. Bunnings has the correct photo.
The BRITA On Tap Water Filter System easily attaches to your kitchen tap, there is no need for a plumber or tools. You will have great tasting BRITA filtered water instantly
Easy to install, no tools or plumber needed
Great tasting BRITA filtered water
Lever to select filtered water or tap water
Activated carbon block technology
1200 litre filtered water capacity
They don't look like identical items based on the photos. How are you going to get it price matched at Bunnings?