BUD-SYD on November 17 is 659 USD on Skyscanner / GotoGate. I've never seen anything that low for Europe-Australia. I do not know which fare classes this falls into but I suspect it must be the 25% which makes it less desired for a mileage run.

Edit2: yes, it's Air Serbia via Belgrade and Abu Dhabi, the long haul AUH-SYD leg is by Etihad.

Edit: also, LHR-SYD on China Southern return often is $1100 or just below but I think that earns zero miles which is a pity because it's 2.5c...