We have just completed our knock down rebuild and moved into our new house 2 weeks ago and are really happy with our new home. We are in Victoria and the whole process took approx 15 months.
The demolition cost for our 2bdr weatherboard was $8,800 and $2,400 for tree removal. We built with a small family builder, our dble storey 24sq house plus 4sq alfresco area cost $283,000. They had a 320 day build time in the contract and it was completed 4 days after this date.
One thing I would suggest is to have it inspected at each stage by a private building inspector as ours picked up issues that we didn't know about and we were able to get it fixed by the builder at each stage.