What is the weight of the bulletproof cockpit doors of a Boeing 747?
From federalregister.gov:


  The FAA also assumed that the average safety door system adds 100 pounds to a large airplane. This additional weight would have minimal impacts on weight and distance limitations.


For a large airplane, like say the 747, it seems the weight addition is around 100 lb (including the other safety features such as the surveillance). As for the exact weight before/after, this information is not readily available as the doors are not sold to the public. But feel free to get in touch with Boeing if it's for research/educational purposes and such.

If the information provided by the seller on this eBay item is correct, then the weight of a 747-400 door is 59 lb. And also from eBay, is a bullet proof 737 door shown below.