During his first decade in New York City, David A. McKnight lived in rentals downtown. But three years ago, when he was renting in the financial district, he decided to start saving to buy something.

“It didn’t make sense to pay more than $3,000 a month to rent in FiDi,” said Mr. McKnight, whose business, McKnight Image Lab, offers image consulting, interior styling and life coaching. So he migrated north to Harlem, where he could not only lower his rent, but also “get to know the neighborhood and start eyeing places to buy.”

Mr. McKnight, 46, who is originally from Trenton, N.J., rented a one-bedroom in a condominium building, paying $2,000 a month and planning to stay until he found the right place. A year later, his landlady unexpectedly put the unit on the market, asking $595,000.