Perhaps someone with more knowledge on the subject than myself would care to chime in

I was just perusing eBay, looking at the prices that PF70 Presidential Dollars are fetching, and I am just floored. There's currently 2-3 sets of all 4 2007-S Dollars graded PF70UC by NGC that has a current high bid of close to or over $1,100.00

Given that there's no census out there (at least on this site) for Presidential Dollars, how can these coins command that high a premium?

Obviously, there's another source or sources of information that is driving these prices. I'm just curious as to what that could be.