First, I love how they figured out how to source the materials for building a Death Star. Based on their calculations 1.08×1015 tons of steel is needed. Luckily, the Earth has plenty – enough for 2 billion Death Stars.
“But, before you go off to start building your apocalyptic weapon, do bear in mind two things. Firstly, the two billion death stars is mostly from the Earth’s core which we would all really rather you didn’t remove. And secondly, at today’s rate of steel production (1.3 billion tonnes annually), it would take 833,315 years to produce enough steel to begin work. So once someone notices what you’re up to, you have to fend them off for 800 millennia before you have a chance to fight back. In context, it takes under an hour to get the steel for HMS Illustrious.”
It’s a lot. But they ignore all the ancillary costs like design, construction labor (unless you’re the Empire and get “free” forced Wookie labor), and furnishings. Yes, furnishings.