Oh boy, I remember 10 years ago living in SF and renting out an alcove in our 3 bedroom apartment for $350/month. It was a 10 foot by 10 foot nook off a hallway without a door. That was after converting the living room to an extra bedroom. All to pay the monthly rent (no profiting). Fun times though!
I kid you not that people in SF both live in storage units (with power, cooking, fridge, and TV) and rent walk-in closets to live in.