Buy 2 Echo Dots (2nd Gen) for $49 on Amazon Australia.
From T&C's:
This Offer is valid to 11:59pm AEDT on Monday 31 December 2018.
Edit: 1/1/19 - Deal still running (Thanks AussieDaddy)
This offer (the “Offer”) applies to
customers who purchase in a single order, 2 Amazon Echo Dots (2nd generation) (Black B07456NHZ6 or White B0745757C9) (“Qualifying Items”) on Amazon.com.au will receive those 2 Qualifying Items for $49.
I prefer these to the Google Home minis. The aux out really helps improve its usage case.