Most short-term do-it-yourself radon test kits cost between $10 and $20, and long-term kits generally cost between $20 and $50. The kits sold by the local health departments include the price of the test device, the postage to mail it back to a lab out of state, and the lab fees for having the device analyzed. Most kits sold in retail stores or through mail order also include everything in the price, but a few companies charge extra for postage or analysis, so be sure you know what you're getting before you make the purchase!
People involved in real estate transactions often prefer to have a professional perform the measurement for them. Test prices vary depending on the device or instrumentation used by the tester, travel costs, and so on, but the price would generally range from $50 to $150. Be sure the tester you hire understands and follows the testing protocol. (Testers are not licensed in Michigan, but you are encouraged to use an individual certified by either the National Environmental Health Association (NEHA) or the National Radon Safety Board (NRSB). Contact your local health department for a list of measurement companies or visit the organization websites.)