This extremely limited 1976 Mickey Mantle Card is almost impossible to find in a Gem Mint 10 grade.  Only 3 exist (POP 3), and I own 2 of them (and one is staying in my private collection).  The third is listed at $1999 on ebay right now.  How limited is this card?  Here is the SGA POP breakdown 
PSA 10                           3
PSA 9                             2 (both owned by me)
PSA 8                             0
PSA 7                             2
PSA6                              1

Thats it.  8 PSA graded cards exist, and only 3 are Gem Mint 10's.  

I don't know what this card is worth, no one does.  The buyer and I will set the market together, and guess what, I am asking 10% less than the other guy.  Make me an offer I can live with, and lets set the Mickey Mantle Market together.