Private islands in New York can cost up to $3 million, according to Private Islands Online, an online marketplace listing private island sales. But Columbia Island in New Rochelle, New York, about 30 minutes from Manhattan, is on the market for $13 million. For 11 years, the current 85-year-old owner Al Sutton, a real estate developer and former physician, spent $8 million to build a sustainable home on the island, according to Robb Report, with the intention to potentially live in it. "I was more ambitious when I purchased it," Sutton tells CNBC Make It, "and now in my 80s, it's not as practical," so he is selling it.

Julia B. Fee Sotheby's International Realty

The home is built on bedrock, which is the same geologic feature that supports Manhattan skyscrapers that provides stability, according to a representative from Sotheby's International Realty, the agency handling the listing, and is surrounded by a 5-foot seawall and landscape decking for storm and flood protection. The home is self sufficient. It has solar panels for electricity and diesel generator back-ups; a reverse osmosis water filtration and desalination system for clean water; in-floor radiant heat with boilers and hot water-heat exchanger; and a sewage system. Another reason for the high price is the location, according to Sutton. The island is about 30 minutes "fast boat" to East 34th Street heliport, according to Bloomberg.

Julia B. Fee Sotheby's International Realty

The 5,600-square-foot home on Columbia Island has four bedrooms and two bathrooms, as well as an open kitchen and dining area overlooking Long Island Sound, according to the listing.

Julia B. Fee Sotheby's International Realty

There is a great room "with views from every angle."

Julia B. Fee Sotheby's International Realty

The master bedroom has large windows for views, as pictured in the rendering below. The master bathroom has a large rain shower, as seen in the rendering.

Rendering of the bedroom. Julia B. Fee Sotheby's International Realty

Rendering of the bathroom. Julia B. Fee Sotheby's International Realty

The home has a private dock. The island is only accessible by boat.

Julia B. Fee Sotheby's International Realty