As everyone in Japan now knows, there are millions of vacant houses and apartments throughout the country, many of which are on sale for a song. The money and effort needed to renovate these properties, however, often isn't worth it given how inexpensive new houses can be. That, of course, is the main reason why there are so many vacant homes in the first place. With the Airbnb boom, people may think they can buy some of these cheap residences, fix them up and make a killing by renting them out to tourists. However, 75 percent of the Airbnb listings in Japan are in Tokyo, Osaka and Kyoto, cities where property remains expensive, and 70 percent of all listings are apartments and condos.

There is one area of potential: resort condos, one of the most depressed real estate markets in Japan. During the bubble years, tens of thousands of units were built in onsen (hot-spring) resorts and ski areas, and they sold very well. Eventually, though, the ski boom ended, and after the bubble burst and the economy contracted, most owners realized they couldn't afford a second home. Even when they could, they found they didn't have the time to use these vacation homes effectively.

The major housing portal sites in Japan list thousands of used resort condominiums, with prices going as low as ¥100,000. In order to put that sort of number in perspective it's helpful to first look at cheap non-resort condos in the Tokyo metropolitan area.