I LOLd but then had to do the math. Turns out that the dry weight of a SpaceX Merlin engine, in gold, costs almost exactly the same as a production RS-25.

Current spot price of gold is $1800/oz. Merlin dry weight is 1380 pounds. 1380 pounds of gold is right at 40 million dollars.

Per https://en.wikipedia.org/wiki/RS-25#Space_Shuttle_program :

"A total of 46 reusable RS-25 engines, each costing around US$40 million, were flown during the Space Shuttle program"

Beautiful.