At $2.2 billion in 1945 dollars for the WW2 super project, Feinstein estimates the 20-year cost to complete the Death Star at more than $192 quintillion (that's 18 zeros).
How much material does it take to make a Death Star?
Applying that steel density to the Death Star's size--the moon-size weapon was reportedly 140 km in diameter--they determined that just over a quadrillion tons of steel (quadrillion comes after trillion) would be required for construction.