Here's what's surprising - there's enough iron on Earth to make 2 million Death Stars. Sure, it comes from the core and would ruin the planet completely if it was removed but who needs Earth when you have 2 million Death Stars?
As for the cost, they estimated the cost of the iron to be $852,000,000,000,000,000. That's 13,000 times the Earth's total GDP.
What they DIDN'T figure in was the cost of getting the iron into outer space, let alone the electronics and paying all the space contractors to build the think. Space unions have very good salary and benefits negotiators. So I'd add about 15 zeros onto that cost. But, hey, the good thing that unemployment would be reduced to zero! Economy problem solved by the Empire!