You need to engage a quantity surveyor

as a rough guide think ballpark $450-500K depending upon various decisions and selections

I did a recent feasibility on a similar scenario and a builder confirmed this was accurate, and that was conservative. If you are integrating any services (eg hydronic heating) or have any feature elements this will need to be accounted for. If you want super accurate costings as Kate said you'll need to get this quantified professionally, which typically requires some degree of professionally detailed documentation as opposed to basic plans

I just did exactly the same scope, excluding changing the whole floorboard, and it lands at 450k. Mind you that I am doing it as owner builder and most of the tradies are my clients. We got really discounted mates rates of everything. For anyone not in the industry, expect around 480-500k for a medium-high quality finish.

Yep