Private islands come in all shapes and sizes and can cost anywhere from $200,000 to $200 million, depending on what you're looking for. However, buying an island and building on it is a major investment of both time and money, so it's important to find the right one that's worth waiting for.

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.

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.

John Mallone – Sampson Cay, Exuma Bahamas John Malone is the largest private land owner in the US – owning over 2.2 million acres of land through the United States. 31 of the acres he owns are Sampson Cay, an island in the Exuma chain the Bahamas. Sampson Cay is complete with a resort and a yacht marina.