In real life you can buy land on Mars for $25. It violates the United Nations Office for Outer Space Affairs' Outer Space Treaty, (2222 (XXI). Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies), Article II, Section One, "Outer space, including the moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means." But I'm sure someone can find a loophole.
Update: I found a loop hole. A couple years after The Outer Space Treaty was published, Stephen Gorove published: Interpreting Article II of The Outer Space Treaty. It states "Under such interpretation the establishment of a permanent settlement or the carrying out of com- mercial activities by nationals of a country on a celestial body may constitute national appropriation if the activities take place under the supreme authority (sovereignty) of the state." This is saying that someone from a country cannot carry out commercial activities by the will of said country. So you can't carry out commercial activities if the leading power tells you to. This means that since the current United States president did not tell me to sell land on Mars, I can sell land on Mars, without violating The Outer Space Treaty, if I so chose.
Luke Skywalker (To keep this comment on topic)
