What is the average annual salary for an assassin?

As said of the JFK assassination and recited in the movie "Star Trek VI", the first rule of assassination is to kill the assassins. In that case, any payment for work done would not likely be made at all. A good number of assassinations have been done or attempted by persons of unsound mind. In these cases, payment would be to be crazy and in jail, or crazy and hung. If you are a Navy Seal or in the SAS, it's standard hazardous duty pay. As for the CIA, KGB or the British SIS (aka MI6), I would guess they are simply on salary. Since the military and intelligence agencies are not known as high paying organizations, I would guess the answer is "not much".

I wouldn't regard "hit men" as assassins but simply paid murderers. However, contrary to Hollywood scripting, they are paid a rather paltry sum and are not usually offered a lot of work. Actor Woody Harrrelson's father was a hitman who died in prison in 2007. This fate is part of the usual retirement plan for this profession. He both boasted of and denied an involvement in the JFK assasination. He has been regarded as one of "the three tramps" found in a boxcar behind the grassy knoll. While their photographs exist - three clean shaven, well-dressed tramps - the arrest records, fingerprints, etc. were somehow "lost" by the Dallas Police.

The Word assassin dates back to the First Crusade with Hassan-i-Sabbah and his Fida'i (suicide agents). It's early etymology came from Marco Polo who reported that in his mountain-top stronghold Sabbah would drug his agents with hashish, lead them to a heavenly garden where they would be entertained and told that if they carried out their assignment they would be transported to an even better version in Paradise when killed. Thus the Word assassin was thought to come from "hashishin", the usual Arabic translation of "assassin". This is now generally regarded as incorrect although no written record remains as Mongols burned the library of the Assassins in 1257.