• First, assume that 1/10 of the 17.16 quadrillion cubic meters of the Death Star is something other than empty space and 6/10 of the total volume is pressurized space.
• That will require 1.71 quadrillion cubic meters of steel, about 134 quadrillion tonnes. That's $12.95 quintillion in current 2008 prices, and that's without counting strange alloys and elements.
• Shipping that to space will cost $95 million per tonne: So add $12.79 Septillion in transport.
• Now you need to add air, which will require 8.23 quintillion cubic meters of Nitrogen, and 1.65 quintillion cubic meters of oxygen, for a total delivery cost of $2.81 Septillions and $212.46 quintillion.
The total: $15,602,022,489,829,821,422,840,226.94.
So the current GDP of the entire world is somewhere $61 Trillion Dollars. That's $15 Octillion Dollars. Or about 200 Trillion times the current Earth Economic Output. You'd really need a Galactic Empire to afford one of these things...
Source -- Gizmodo and Ryszard Gold