Ron Guth:
In 1869, the Philadelphia Mint produced only 600 Proof Silver Dollars. They are generally considered to be common in the sense that they are readily available to collectors in a variety of grades at reasonable prices. PR63 and PR64 examples are the most frequently-seen grades. Gems are rare and are almost never seen above PR65. In fact, the best examples known of this date are a single PR67DCAM.
Approximately twenty percent of all Proof 1869 Silver Dollars are Cameos, but fewer than ten percent are Deep Cameos.