We are going through this at the moment - I bought the house 8 years ago and it's more cost effective to knock down and rebuild than to try and renovate or sell & buy something equivalent to what we are building since we are only 6km's from CBD. We aren't subdividing though.

Demolition - $10K
House - 3 bedrooms, 2 bathrooms + study $265K - when we sat down with builder we told them everything we wanted included such as luxuries as stone bench tops/floor to ceiling tiling in bathrooms/ extra coat of paint etc in price so we weren't hit with any hidden extra's and we could take out if we needed to reduce cost
Extra's - flooring, blinds, aircon/heating, rainwater tanks, driveway, fencing etc $50K