Get a direct quote from a Builder (with own team of workers), usually a landed specialist.
Too many times, too many wanna be builders are actually your run-of-the-mill reno contractors.
Nothing wrong with engaging a reno contractor for reno work. But your general reno contractors would not have the experience to do structural work and would usually have to sub it out. That's where u see the padded costs added on.
I had a lot of PM advise from various forummers here like Yap, Lee, Wai and others.
Each of them approach their landed build in a slightly different manner, but their common key is in finding the right builder/architect/contractor that they can work with.
For major reno for landed, more is less and less is usually less. Meaning once u hit a budget of couple of 100ks... u can usually do a lot for more for what u spend.
The margin for the builder would already be priced in and depending on your relationship with the builder, he can usually bundle in extras for little or no cost to u, its really whether he want to make u pay for it or not. U are not buying a pasar malam product, its important to have a good understanding with your builder/main con.
U will be surprised when u fully itemized out all the items.. u will find the quote will usually be doubled if the work is divided up into separate reno quotes.
For value for landed, I recommend u either spend minimal to do the minimal or go all the way build to your maximum allowed enveloped. Spend the bulk of the budget on the wetworks first, u always do the carpentry at a later stage. Increasing your GFA(GrossFloorArea) would usually increase your valuation, adding a 10k gold plated showerhead will not..