Earlier quoted context omitted.
hah. gold is not that rare. even an entry level billionaire could afford a monolith this size
Printer ink then ;-) On a more serious note, Rhodium fits the bill: super expensive, hard, durable, silvery and corrosion resistant. Using the 7,700 lbs estimate elsewhere here, and a price of Rhodium I randomly found on the internet of $16,100 per troy oz, the material of this structure, if made from Rhodium, would cost about $1,749,005. Which is actually not bad, for a very rich person. I guess they'd have to build…
[0]: 7700 lb * 14.5833 troy oz/lb * 16100 $/troy oz = 1,807,891,701