Looks like these SodaKing bottles are on 30% off for those looking to stock up/refill for the holiday season, seems to be the lowest they ever go:
https://www.ozbargain.com.au/node/571962
Here is the link to the full bottle if required:
https://www.spotlightstores.com/kitchen-and-dining/kitchen-a…
As previously mentioned the smaller valve (SodaKing and Kegland) are apparently very easy for DIY refill compared to the larger brass valve in the new Sodastream.
Dont know if it just me but the Soda King bottles have a different tasting gas than Soda Stream (meaning they taste kind of weird)