Hey! This is the article I wanted to write! Yes, colonizing the ocean would indeed be much cheaper and livable than colonizing a planet or moon. But each would nevertheless be expensive and marginally livable by human standards. The point of each would be to gain access to valuable minerals and food sources, I suppose (and that's where ocean living would be advantageous?) If one subscribes to the "20,000 Leagues Under the Ocean" concept, there might be advantages in an ocean based colony, perhaps floating (so as to not deal with the great pressures of the deep) and also connected to some kind of transportation tube with the mainland? The residents would then have access to the surface for occasional sunlight and air while taking trips to the deep to mine rare earths or whatever is down there. They could also "farm" fish, and there would be military advantages. Of course, this already sounds like life on an oil platform, and kind of dreary. Besides, aren't there potentials for plenty of rare earth mines/fish farms/military bases at/near the mainland? I suppose the real value of a planetary/ocean colony would be as a "way-station" to someplace else (another planet/moon, or in the ocean's case, two continents)