The house I purchased a few years ago had elevated radon levels. Seller was required to have a mitigation system installed. I don't know who he used, but I believe the cost was less than 3K. They drill a hole.in your basement floor and shove a pipe into it and run it through an outside wall, connected to a small fan that draws the air out of the soil and expels it above your roof line. A quick Google search for radon contractors will get you started. But before you go all in on a system, run a few more tests. You can hire a company to set up a machine that samples the air over a 24 or 48 hour period and get accurate level measurements. Cost for this test was a couple hundred bucks three years ago.