I checked the online fare prices for a "milk run" to Brisbane to Bali early March (for example), flying 3 budget airlines. I didn't tie up times and a stop over would probably be required, but the result was interesting. All fares are in AUD. Some extra taxes aren't shown.
Brisbane to Darwin on Virgin $119. Darwin to Singapore on Tigerair $37. Singapore to Denpasar on Valuair $90. Total $246
Return fares are the same, giving a total return fare of $492!!