Just how wealthy would the Empire have to be to build a Death Star? Well, wealthy enough to blow somewhere around $852 quadrillion on metal alone, according to a group of economics students at Lehigh University. How did they get that number? Well, the first Death Star has a reported diameter of about 87 miles. They decided to assume that it was made of steel, and was roughly as dense as a modern warship, according to this Centives post spotted by ShortList.
If that's true, they calculate that it would require 1.08 x 1015 metric tons of steel to build the thing. The good news is that there is actually enough iron on Earth to handle that—indeed, there's enough to make 2 billion Death Stars. The bad news? Based on the world's current output it would take 833,315 years to turn enough of that iron into steel, and it would cost the aforementioned $852,000,000,000,000,000. Which is to say, 13,000 times more than the world's GDP.