Class of travel? For travel March 2023 (~10 months out) current pricing will not be the lowest. Fares can rise and fall.
MEL/SYD to PER can be expensive,
QF & JQ can also get you to PER.
For domestic AU flights I have never experienced multi city cheaper than separate point to point. In AU air fares are generally the sum of the components.
A map from Great Circle Mapper - Great Circle Mapper