SYD-SIN - Carrier imposed surcharge for cash bookings
On Emirates : $0
On Qantas : YR $17.50 non stop or $35 via Melbourne

Actual taxes non stop $92.22 , via Melbourne $79.45

Where does the other $228.55 come from

Unless Qantas has started publishing a co-payment requirement for award travel, there seems to be something very untoward going on