Bhai ... best sound deadening material, the industry standard, is Dynamat. It is very very expensive. I checked its price in Islamabad ... it was 23500 for a box of Dynamat Extreme Bulk pack. It is 6ft X 6 ft. It is very heavy and dense material. The bulk pack weighs 8 kg and thickness of the butyl rubber is 1.7 mm.
Right now I have done some temporary sound deadening which includes butyl rubber pasted on the inside of the outer body shell. In case of doors, I have used waterproof jumbolan between the inner metal door shell and the plastic trims.
There is another product, Peel&Seal, which costs about 20% of the cost of expensive Dynamat. I have seen it discussed in a thread on PakWheels .. You can find it. I think, if we have a cost benefit analysis, this is the best suited product for a vehicle not meant for SQ and SQL music.
In my case, I am expecting arrival of two bulk packs of Dynamat from Saudi Arabia .. I dont know for sure how much it will cost, but should be cheaper than in Islamabad.