Missouri gives kits away and says so plainly. The state health department offers short term radon test kits to residents at no cost while supplies last. The phrase worth paying attention to is while supplies last, because that is a real limit rather than boilerplate. Programs funded this way tend to run out, especially in January when radon gets attention and requests jump. If you have been meaning to test, doing it early in the season is often the difference between getting a free kit and buying one. Request yours through the state health department form.