Whenever I'm asked what kind of writing is most lucrative, I have to say, ransom notes. In the past twenty years or so, I've probably written a couple of dozen scripts.
Many writers bang out four or five scripts a year.
Patrick Sheane Duncan has written over eighty in the last twenty years. This is not a new thing. Long before personal computers were even an idea, screenwriter Lindsley Parsons Sr. wrote Desert Trail for John Wayne in five hours back in 1935. You write your ass off. Let me tell you a story about a movie I wrote in five days.