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.
Those numbers are out of date now, they recently restarted production and it turns out each engine is about $150M now for the new production run for the SLS. (Which about the cost of a full expendable Falcon Heavy rocket launch along with all 27 of its Merlin engines.)
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.