The Proof 1942 Dime boasts a tiny mintage and it is the last Proof Dime of the Mercury Head series and the last Proof Dime until coinage of these special coins resumed in 1950. Large quantities of these Proofs are available for collectors (PCGS alone has certified obver 5,700 examples alone as of June 2015) in a wide variety of grades. PR64 to PR67 examples are plentiful and affordable. In PR68, this dates becomes rare. In April 2015, PCGS graded a PR69 1942 Dime, one of the most incredible survivors of this date -- the coin has monster toning and killer eye appeal (to use popular numismatic vernacular).
No Cameo or Deep Cameo examples exist and any coins offered as such should be examined carefully for doctoring.