The movie’s plot was so convoluted it made my head hurt–in a good way. Meanwhile there are people arguing about what the hell actually happened in the movie, which is maybe not so good.
I spent a year writng an annotated version of Rosemary’s Baby.
The apartment was rent controlled, renting for $320 a month. High rent, but not out of control, even back in 1965. Guy was getting resiiduals from a series of Anacin commercials and also did other commercials and a reoccuring character on the soap Another World to pay the rent while waiting for the big break.
Also, Guy & Rosemary had been living in his studio apartment for the three years of their marriage, and before that she had shared an apartment with three other “working girls.” So they probably had some money saved.
Quite agree. And he was particularly notable for his huge output - book after book for decades, usually several a year, full of brilliant plots and memorable characters. His Parker books (under the nom de plume Richard Stark) are fantastic examples. Wish he was still around to thrill us. 
English thriller writer Ken Follett is my contribution to the thread - he gives his characters difficult problems to solve and astonishes the reader with the brilliance of the solutions they come up with, usually under very trying conditions. Not a deus ex machina in sight :D. And like Westlake/Stark, he’s been doing it consistently for decades.
Said it before and I’ll say it again: I would love to get a copy of this! Any idea if or when it might be available?
Alas, it might not have survived my moves. I did try to get it published, but failed.
If I ever find it, or redo it, I’ll definitely let you know.