Future Sky Cranes?
Jack McKenna, former Exec VP at SA who pushed the Crane, ABC and S-67, wrote a 2010 book: " Sky Crane, Igor Sikorsky's Last Vision " and at the end proposes a new 20 ton payload Crane design based on the 53K drive train!
Here is US Army cost data from page 47: " The CH-54A's cost the Army $2,847,303 each and the CH-54B's cost $3,014,803 each." ( 1967-72 ). He goes on to write that 40 years later, a surplus CH-54 in remanufactured and updated condition has gone for $28 million.