Appears to be a pricing error - search fares using Google Flights, then book via the Qantas website.
Obviously a chance that the airline will cancel these fares, but worth a shot - if they cancel, they will refund. Just don't book any onward travel or nonrefundable expenses until the situation is clearer.
Thanks for this. Did you manage to book for this price? When I click through to Qantas to book, it goes back up to $2000+. I think Google flights may be picking up on a promotion - buy one way, get the return for $100 etc. and then showing the lowest prices as 2 x $100?