Scoot - Athens Return from Perth/Gold Coast/Melbourne/Sydney from $597/$617/$637/$637, or Berlin Return from $684/$638/$678/$678
Scoot has some great prices here. Seriously, they're a budget airline and adding in bags and food will hurt you, but if you're prepared, pack light and don't mind the long haul, you can't beat this price to Europe.
From: Perth/Gold Coast/Melbourne/Sydney from $597/ $617/ $637/ $637
From: Perth/Gold Coast/Melbourne/Sydney to Berlin from $684/638/ $678/ $678
Dates: various from Feb to May.
Found on Flightscout initially (eg https://flightscout.co/au/cheap-flights/anywhere-to-athens-g...), but upon going to Scoot's website could get a bit cheaper on some dates, especially if the coupon code is applied.