I've searched various strings along the lines of NYPD + history, NYPD + 1940s/1950s, NYPD/police/cop + salary/wage, 1950s/1940s + salary/wage, history + salary/wage, etc. I've managed to find current and 19th century NYPD salaries, sample incomes for other jobs in the late 40s/early 50s, and 1950s salaries for police officers in non-US countries, but nothing in the sweet spot yet.
It may be a long shot, but I'm hoping someone at least has a ballpark estimate.
ETA: I managed to turn up an estimate of about $2500 a year for a patrolman with the SJPD. If anyone happens to know whether the NYPD paid more or less than that at the time, please do chime in. Otherwise, I'll take this as a guideline.