I find burning Avios in Oz pretty good value. A couple of random dates in December show biz availability from PER to SYD for 34k plus £39 tax, although you have to go via MEL. December of course is peak holiday time in Oz, so reward availability in the area, particularly places like Bali, can be difficult. Also cash tickets become expensive as well. It sounds like a brilliant trip and hope you get it sorted.