Cost for Radon Mitigation. Radon gas is odorless, colorless and radioactive. It comes from the breakdown of uranium, which is present in the soil, water and natural gas in many areas of the country. According to the EPA, radon gas is the second leading cause of lung cancer.here are different types of radon tests. Only a licensed radon tester can perform such a test, and a homeowner can expect to pay around $200. The average cost of testing and installation of a radon mitigation system is $758, explains the Home Advisor website.