The 1973-S Proof Kennedy Half Dollar is one of the more common Proof coins in the series. Most mintages in the 1960's to 1980's are in the 3 million range more or less. Once you get into the year 1993, mintages for some years drop under 1 million.
The 1973-S Proof Kennedy Half is very common in most grades even in PR69 Deep Cameo. Only in perfect PR70 Deep Cameo are they very scarce.