Buy a radon vent fan if this makes you feel better, but most houses don't need them. You should first have the test for radon done and then make your decision. People have been living with and breathing radon gas since there have been people on earth.
For some reason there is this wide spread fear of radon when there are no studies of any significance that can say that breathing radon gas has lead to an increase in cancer in people. Most studies have shown that there is no increased risk of cancer because of radon gas in houses.
Like I said, buy the radon gas fan if that makes you feel better, but chances are you don't need it.