The 1999 $10 Mint State Platinum Eagle is one of the more common dates in the $10 Mint State Platinum Eagle series. It's mintage is approximately 56,000. Several other $10 Mint State Platinum Eagles have mintages under 15,000.
Therefore, the 1999 $10 Platinum Eagle trades very close to the spot price of Platinum and it is one of the easier dates to find in the market. The majority of examples range between MS68-MS69 condition.