So, we did a second radon test, which came back with a lower level than the first test but still above what's recommended, so we asked a friend for a recommendation, then contacted Radon Removal, who provided us with this:
My lovely assistant is gesturing toward the fan, which runs constantly and is very quiet. With some houses, they're able to run the chimney inside the house and put the fan in an attic or a closet, but our house is very small and there simply wasn't an inconspicuous place inside.
Here you can see the pipe in the basement, next to our furnace.
And here's where it goes into the floor. They drill through the floor, suck out some dirt and sand, then seal in the pipe, which draws radon from beneath the house.
The cost was $1375, and the installers were fast and friendly, so we're pleased. I've mailed off the follow-up test to see just how much of a difference this'll make. I'll post that when it arrives.