Bob Orben, quoting Dai Vernon, gives credit to Judson Cole for the phrase in Genii
Fred Allen and [Judson] Cole were having lunch together and Allen was concerned over a bit for his radio show. He had to describe a young lady of easy virtue and wanted to do it in a humorous way. Jud thought a moment, then said: "Why not call her a girl with negotiable affections?"
However, a 9/26/1937 review in the Washington Post
of the book Harbor Nights
by Harvy Klemmer uses the phrase, and I wouldn't be surprised if it were to be found in Klemmer's book.