Islands in the Oceania region are more expensive at $18,537 on average per acre, while they are $23,516 on average per acre in North America. Europe ranks as the second most expensive continent to purchase a private island, with the average cost per acre over $68,000.

Some islands can be bought undeveloped, while others already have roads and/or houses. Islands are also available for rent. Many celebrities have their own private islands. Commercial development of uninhabited islands can raise ecological concerns, as many have a fragile environment.

Krolow owns several islands in places like Canada and the Caribbean. He said the rentals of those properties act as a key revenue stream, forming around 25% of his annual income — the rest comes from commission he makes off of island sales.

You can find private islands for sale via Private Islands Inc. or Vladi Private Islands, or by contacting a realtor who specializes in big-ticket sales. Additionally, some high-end real estate companies, like Sotheby's International Realty or Christie's International Real Estate, list private islands for sale.