I’ve seen basement closets for $700+/month that didn’t have windows or a kitchen.

Huh. Fun fact, the International Building Code is a "model code" that's adopted as the basis for building code by most jurisdictions in the USA. Meaning if you're in the USA it's more likely-than-not code where you live.

Another fun fact: there are egress requirements for basement that contain "sleeping rooms" (R310.1). Essentially, you need a minimum 1 normal means of egress and 1 emergency escape and rescue opening unless the building is equipped with an automatic sprinkler system -- and your local code might have even stricter requirements.

This is a disturbingly common code violation by people trying to rent out their basement. It would be a real shame if someone were to read up on their local code and report suspected illegal basement conversions to local code enforcement or the fire inspector.