About 15,000,000,000,000 times as much as the current (and controversial) U.S. economic stimulus bill. And that's a conservative estimate...sort of.
When the original Death Star was destroyed, Emperor Palpatine apocryphally asked of Darth Vader, "Do you have any idea what this is going to do to my credit?" (I saw it on Robot Chicken, so it must be true.) Now, even though the entire treasury of the Galactic Republic was at his disposal, Darth Sidious was right to be perturbed, as — by at least one estimate — the Death Star cost about 15,000,000,000,000 times as much as the current (and controversial) U.S. economic stimulus bill.
And that's a conservative estimate...sort of. Setting aside that you can't really put a price tag on the power to blow up planets — which requires about a billion-trillion times as much energy as can be generated by the United States — there is a very general way to estimate what it would cost us, right now, in current U.S. dollars, to build our own Death Star.
"(The Death Star has) a volume of 17.16 quadrillion cubic meters. At 1/10 volume, we'll need 1.71 Quadrillion cubic meters of steel, weighing in at 134 quadrillion tonnes. In 2008 steel products, from wire to ingots were selling for an average of $962 per tonne, so our cost of steel alone is $12.95 quintillion. Now, how about getting that into space? According to the numbers I could find on the internet, it costs around $95 million to ship 1 tonne of materials into space, so that means we'll be cutting NASA a cheque for $12.79 septillion."
A septillion is a 1 with 24 zeroes, or a trillion trillions. Call it the stimulus bill squared.
Now, this Death Star estimate makes some pretty glaringly wrong assumptions. First, we have no idea what the Death Star was made out of, and the Empire very clearly had technology (antigravity, hyperdrives, astromech droids, VGA targeting computer graphics) that we can't use, and that almost certainly made the job of building a Death Star easier (read: possible).
Second, I rather doubt there are 134 quadrillion tonnes of steel to be bought on the open market (or possibly even on the planet). World steel production is in the neighborhood of 1.3 billion tons annually. That means it would take over a million years just to produce that much steel at current global production levels, and we'd probably run out of raw materials before then. Also, the union labor costs would be killer, especially compared to the costs of mining droids or Imperial wookiee slave wages. And even if you could buy that much steel, doing so would almost certainly destabilize the market for steel so severely that the price would spike well beyond the 2008 average.
The same destabilizing factors would apply to the spaceflight costs. The Saturn V is about the only human space vehicle that could deliver large payloads beyond low Earth orbit. The Saturn V could get about 50 tons of payload to the moon, which means we'd need 2.7 quadrillion Saturn Vs to launch that much steel into space. Considering that we've only ever launched 13 Saturn Vs, that seems unlikely. The proposed Ares V launch vehicle for Project Constellation will supposedly triple the Saturn V's payload capacity, so we'd only need 900 trillion of those. If we launched one Ares V every second, it would only take about 28.5 million years to get them all into space.
And all of that is just putting raw materials into space, with no heed paid to design, assembly, systems integration, or operational expenses. In most construction cases, materials represent about one third of total project costs, so at the very least, a Death Star would actually run you about 50 septillion dollars. Conservatively. But since it's going to take around 30 million years to complete the whole project, we've got time to save up.
(Found via Geekologie.)