There is no definitive answer to the question above. As the costs vary from house to house.
Depending on the space, whether it's a 3 room, 4 room, 5room, Executive or even a Maisonette. The price will vary depending on what you're going to do to it.
For example, a whole-house renovation for a 5-room resale flat that includes the flooring, kitchen, 2 toilets, whole house windows, rewiring, and carpentry for the whole house can go up to $70,000 these days. You can imagine what the price is for the same scope of work for an Executive or even a Maisonette unit.
While the above have not taken into consideration your sanitary fittings and air conditioning units, these alone can cost you anything from $2000 up to $9000 or even more depending on the range of items that you choose.
For example, an instant heater shower set will definitely cost lesser than a mixer shower set. A mixer is a sanitary fitting that is used for hot/cold with a storage heater tank unit.
The price can go up more when you include works such as plastering of the walls and ceiling. And also doing Lbox with cove to spruce up your ceiling space.
So, the actual costs of renovation really depend on what you need to do vs what you want to do for your space while balancing the budget that you have for your renovation and also for the furnishings later on.