Tokyo Metropolitan Government Building

The Tokyo Metropolitan government has gotten into the skyscraper building excitement as they have their offices in a 50-some story building in Shinjuku area of the City.
The observation deck was free and came highly recommended by the Lonely Planet Guidebook that was my companion on this trip. The new Tokyo Tower is being built further off into the distance as seen in this picture. That building is supposed to be the tallest in Japan when it is completed.
The picture shows it's clearly dwarfing the other major buildings throughout the landscape. After 9/11, I am not sure I would want to be in the tallest building in the world on a daily basis. I am quite content with the third or fourth place one. There's the flip side to that which would suggest we need to build these...

The TMG as it is described on the sign out front has two towers. you can see the other on the left in this picture and the model in the next photo. The architecture of the building was unique with lots of different building facades that made it look like a computer chip of sorts (per Loneley Planet).

I'd like to know how much these buildings cost to construct as opposed to two smaller ones that would hold the same space. It seems like there's an environmental aspect to these buildings that at some height they become significantly harder to construct, but I am not an architect.