The cost of the Death Star is near and dear to my heart. Recently OVO Energy has worked on calculating the operational costs of running the Death Star for a single day. The majority of these costs will come in the form of the energy required to use the weaponry and jump to hyperspace. That is, the cost with current Earth technology to produce the requisite power output.
However, the power output is a function of technology and not just raw materials. The mere presence of regular hyperspace travel proves that a new energy source is available at extremely low cost. Thus while the 1032J of energy required for the Death Star’s laser would cost approximately £4.1666667×1024 using current Earth technology, it would be a significantly smaller fraction of the Galactic economy to produce. Consider that the Millennium Falcon is a “piece of junk” and was abandoned on Jakku without being sold for parts, but it is still capable of hyperspace travel. This fact proves that energy costs are no longer the limiting factor and a much smaller fraction of the economy.
That being said: Excited for Rogue One to come out!