Hi best of luck with your decision. I've done a couple renovations and have always found that the house itself limits what you can realistically do and given your often dealing with the unknown a lot of your money goes towards fixing or repairing previous work hidden below the surface.
The houses I renovated though were over 100yrs old and in the inner city so surprises were to expected and prices quoted by traddies often ridiculous. I'm starting a new build now and am about to get to site. So far most quotes (apart from tiles) are often the same or less than what we were quoted for a renovation.