Found this on HotdealsUK. It is for the Europe region so unsure if it is able to be played on Steam in Australia. I hope that someone can comment and it can be edited.
FB like gives 5% off.
Credit: https://www.hotukdeals.com/deals/nba-2k18-pc-474-with-cdkeys…
This game cannot be activated using Australian steam accounts — you'll need to run a VPN and have an EU IP address to activate and to launch the game when connected to Steam.
Steam has it for $9.59 USD (~$14 USD) but at least there is no risk when it comes to activation?