Radon is an important issue here in Minnesota as I mentioned in my blog on the subject:http://johnchrisney.com/?p=742 The cost to install a radon mitigation system ranges between $500 to $2,000 , depending upon the home’s configuration, with a generalized average in my experience of around $1,400 or so. You can view a typical installation by clicking here.
The following is a list of radon measurement and mitigation contractors:
Quality Radon Services
The Radon Guys
Leslie H. Mateffy III