In 1971, the U.S. Treasury made available Unciruclated and Proof verisons of the Eisenhower Dollar in 40% silver. These were the first "silver" Dollars since 1935 (or 1964, if one counts the unissued 1964-D Peace Dollar). The Uncirculated versions were packaged in pliofilm and inserted into a heavy-stock, blue envelope. The Proof versions were placed into GSA-type, hard plastic "slabs" inside a slip-case cover with a faux-wood finish. These new coins were an instant success and collectors snapped up nearly 7 million of the Mint State silver dollars.
Many thousands of MS65 and MS66 silver 1971-S Dollars have been certified, and even MS67 examples are common. However, in MS68, this coin becomes a true condition-rarity. The auction price record for this date is $6,900, realized in 2012 when a PCGS MS68 example came onto the market. Considering what "finest knowns" of other series bring, especially those of the 19th century, this seems like a relative bargain.