Moved into new (to us, built in 1980) house 2 years ago. Installed an Airthings radon meter a year ago. Levels get up to 400 Bq/m3 when all the windows are closed. Finally had a radon mitigation system installed. Will hopefully get to much safer level below 100 Bq/m3.
Depends on many factors. If there’s an available sump pump, a radon lid is around $150. A fan is around $150. Between $100 and $300 for pvc, depending on number of elbows and distance. Assuming an open electrical breaker is available, and again depending on distance, $100 to $200 for electrical. $15 for a manometer. $20 for pvc cleaner and cement. $5 for tube of acrylic caulking. Total for parts, assume $500 to $850.
Wothout a sump well, save $150 on lid, but x3 or x4 the pvc. Roughly $300 to $1000. Rental of a Hilti and diamond holesaw bit to add vents to corners of slab. So maybe $300 or so. Total around $600 to $1500, give or take.
This is just parts. Labor will be $1k to $4k depending on location and complexity. If you can do it yourself, it’s a significant savings. With an available sump well, it’s an easy to medium difficulty project. Without one, it gets significantly more complicated.