PCGS has a list of super rarities that they call the Million Dollar Coin Club, many of these coins are unique and never have been sold, others only once or twice in 100 years. With such little prices realized information available, how do they decide the "value estimate"?
Common sense. Thats like saying if the Mona Lisa came up for auction, how would we know it would go for $100 million plus since it hasnt ever appeared at auction. Well common sense tells us, it would go for atleast 100 mil. It's the freaking Mona Lisa.
Ultra rarities have no price guides or history, it will just be whatever people are willing to pay at that moment. Probably closer to a billion given what other art has gone for.
They pull it out of their rear like a lot of their price guide values. In many cases, it is a reflection of what their board of experts wish they could sell their coins for and not true value. Of course there are exceptions.
Super rarities are not priced for what "someone" hopes they could sell something for. The million dollar coin club are mostly coins that have sold publicly for above or basically at 1 million sometime before in the past, others were sold privately. Believe it or not experts and people in the know actually have a better idea of what it would take to pry some of these coins out of a collection but many aren't for sale barring some insanely high can't refuse price. Some of the coins are just estimated grades from known ultra rarities that haven't been graded yet. It would help if some people would look things up before just saying silly things
