Is is just the granny flat he has quoted on, or additional works? Just wondering as I suspect you are probably in a fire overlay area and the new building regs are very strict. As result the cost of doing anything has increased, plus it often means if you renovate your place you need to bring other parts of the house up to spec.

2 years ago we got a quote on extending the living area and adding a bathroom to our bedroom and it came in at $60,000. That was just getting it to a a basic point, as we were going to do the final fit out.