Been a while so this is a largish update:
Bunnings for everything from fibre cement planking to insulation and tank fittings – $1560.70
Stratco for roofing materials and timber battens for ceiling and roofing to be fixed to – $552.12
Ebay to various sellers for a steel fire door and the wood for the framing of the power room – $300
Mitre10 for external flashings – $30.47
Bushmans for the tank – $688
Total project spend is now at $291,038.33
House only is now $77,085.83
Cost per square metre is now $267.66
From here I can confidently predict the house will reach lockup at around $390 per square metre.
The house will be habitable and pass council occupancy standards at roughly $560 per square metre including the off-grid power setup and a 150kL water tank.