In the beginning of 1873, emloyees at the Philadelphia Mint began striking Proof Half Dollars. The first versions were of the No Arrows "Close 3" variety, so-called because the balls of the 3 were so close to each other that they resembled an 8. This was amended later in the year, but not until after the Mint produced 600 Proofs. According to researchers Wiley and Bugert, two different die pairs were used to strike all of the Close 3 Proofs -- a low average of 300 Proofs per die pair. No Open 3, No Arrows Half Dollars were made.
Today, the Proof 1873 Close 3 Half Dollars are fairly common and they can be found in most Proof grades, but especially in a range from PR62 to PR64. Gems are scarce, but it is not until PR67 that this date becomes truly rare. Cameo examples are common and their percentage of the total population will increase over time as more and more coins are regraded (PCGS and NGC did not recognize Cameo ro Deep Cameo examples for many years).