[PC] The Witcher 3: Wild Hunt GOTY US $19.99 (~AU $27.63) @ Steam Store

Still on special at GOG if you prefer DRM free (https://www.ozbargain.com.au/node/414180), but currently cheaper from Steam directly.

FWIW, the GOG version will give you credit which will make the price almost identical, but this saves the hassle of needing to buy something else from GOG to make it back, plus there are likely people who prefer a Steam key.

You can also get the full trilogy for $22.02 USD if you want/need the first and second games: https://store.steampowered.com/bundle/727/The_Witcher_Trilog…, although that doesn't include the expansions to Witcher 3, so you're probably better off getting the GOTY edition then picking up the other two separately.