I know this can be very difficult to answer - what is an average cost per sqm for a basic extension?
I have received quotes for a 60sqm extension - weatehrboard/stumps - it is basically just one large family/meals room built onto the back of the house with a smallish laundry to one side - no access issue, flat block, only one wall to demolish - nothing fancy.
The quotes I have range from around $1,400sqm to $2,800sqm!!!
All the quotes pretty much list the same in regard to what they include (except the dearest one doesn't include painting!)
Event the Archicentre cost guide has a weatherboard extension at $881 - $1,652