@Willem2904: A few things to consider:
1. The coin was produced by the US Mint, but the commemorative colorization of it was done by a third-party after it had been sold into the marketplace. As such, the "mintage" figure of 200 that the seller may be touting is actually just the number of coins that have had the coloring and diamond applied. As ArrowAndRays stated, the number produced by the US Mint is 237,510; it is not a scarce or rare coin.
2. Many collectors consider this type of "enhancement" post-mint damage and consider the coin to have lost its numismatic value. As such, most would value it no higher than its bullion value.
Unless you are particularly fond of the piece or are able to buy it for below its melt value, I would suggest walking away from this one.
Collecting history one coin or medal at a time! (c) commems. All rights reserved.