Can't speak for others, but the one I made was about a year-long process of communicating with BVN to Licence one of his plaster masters & then North American Mint and compiling all the various aspects of the design. The die creation was rather expensive because of the design needs .. then we had to run a minimum number of rounds; which was a little more expensive than the die creation. Then there was minting, which had added expenses due to the individual numbering of the initial run.. then, of course, it was back to the drawing board because we wanted to change the die .. so whole new die..  =)    

Thank BitCoin GOD that people liked them. (also accepting BITCOIN in DEC of 2016 helped).
Not that I wouldn't have mind holding the bag. I am as satisfied with the end result as I am sitting on my own personal horde.

All in all: I would advise anyone interested in making a masterpiece work of art, and are in love with the idea enough that you are willing to invest a tremendous amount of your time and personal expenses in the project to DO IT, but only if you're doing it for yourself - because you could very well get "stuck" holding your very own private currency of sorts. Like everyone always says: DO YOUR OWN RESEARCH and NEVER INVEST MORE THAN YOU CAN AFFORD TO LOOSE  .

These are the guys who minted mine: North American Mint: https://www.northamericanmint.com/custom-minting/