I remember hearing about RP King of Diamonds back in 2005. They had one at the 2006 Pinball Fantasy show in Las Vegas NV. Then there wasn't much news about the machine for about four years. Then in 2010, they finally released the machine and a limited number of the machines went up for sale. At that time only 50 machines were available. I think they had them priced at around $3700.
As I recall, people were complaining that the price of the machine was too high. At $3700, you could buy a modern DMD machine back then.
Pinball News had a very detailed review about the machine:
https://www.pinballnews.com/games/kingofdiamonds/index2.html
They have the first hand built RP King of Diamonds for sale now on Ebay for....... $25K !?!?
ebay.com link: Prototype One Of One Retro Pinball King Of Diamonds Pinball Machine