Couple of hundreds for entire flooring sound proof. Cost also depends on makes/ size and material used.
Start checking with car audio accessories shops in sg for price and material.
Put up your question in appended link if you consider doing it at JB.
https://forums.hardwarezone.com.sg/cars-cars-204/recommendation-reliable-workshops-jb-3637194.html
Thanks!! Hopefully not expensive for my IS250..