To clarify, they aren’t ventilating your cellar - they’re pulling a small vacuum underneath the slab. This prevents radon from seeping up through the slab into your basement, and instead blows it out through that vent pipe. It’s an important distinction because if that vent were running 24/7 sucking heated/cooled air from the living space of your basement (and consequently drawing outside air into your home through every crack and crevice), your HVAC bills would get pretty hefty.
I had one of these systems installed in my current house by the seller; it’s a pretty standard system, and IIRC the cost was $750. The system took readings from 4.something down to 1.something. We’ve been retesting ever couple of years, and it’s still working fine 10 years later.