we recently completed renovations on our home built in 1952 with kitchen, laundry and bathroom added in 1981...replacing all the windows cost about $30,000 plus labour, new architraves and painting, we did almost all the demolition ourselves although the legal removal of asbestos wall linings cost about $4000 and we also spent about $1000 taking other rubbish to the tip!.even in a carefully planned renovation there will will always be surprises..one unexpected structural beam cost $900 plus another $1000 to install.....i again suggest that you divide the house into sections and concentrate on completing the kitchen and living areas (with new windows etc) and then move on to the new bathrooms and bedrooms when funds allow

There are some electricians on Houzz in SA (https://www.houzz.com.au/professionals/electricians/s/Electricians/c/south-australia) Best to contact a handful to compare and see what the going rate is in your area

Why would you stop at pre wire. Are you electricians? In my opinion this would be not cost effective. You choose all your lighting placements and fittings, and builder installs them, easy. If you stop at pre wire, at what stage will the builder, hand over to you. Because with no working lights or power points, oven connection etc etc., the home will not be at practical completion for your final payment, and for the relative authorities to sign off on the build. Have you priced the cost of an electrician to do all the final work. Has the builder deducted an amount from your build to do delete the electrical work?

@Margot @Alistair McLean @Kate Thank you for your feedback, as we all know in Australia, the preferred aspect is for living areas to be placed on the Northern side of the home. This of course conflicts with creating an indoor-outdoor feel with the backyard and taking full advantage of the bush views from the rear (south) of the home. In regards to knockdown and rebuild, to build a similar house, spec and size would cost roughly 750k plus (turn key). This does make sense in some respect, as you could design a house that is 'perfect' with higher ceilings, no beams to consider or to design around, new plumbing, wiring and a more efficient house in general with all the mods and cons that a new house has to offer. However, the site houses a large 400sm under roof double brick house. So the current improvements are worth 250k approx. As long as the renovation cost + existing improvements don't exceed the possible price of a new built then renovating is still the best option. Based on preliminary costing the renovation still stacks up. However, it's really much of a muchness.