I was in an accident recently and one of the wheels has ceased to turn. It appears that the wheel "mount" (not sure if that is the correct term, it's a rod with a ball on the end that attaches the wheel to the axle?) has come out of whatever it was in. The wheel and axle seem fine. How much would something like that cost to fix?

The lower ball joint likely sheared off--it attaches to the steering knuckle. The outer tie-rod end was also likely damaged. Depending upon the car, it shouldn't cost too much ($350). I recommend going with a Moog ball joint and outer tie-rod end. Afterwards, spend $65 and have the alignment checked, in order to set the toe-in. Otherwise, you'll ruin the tires.

What make, model, and year car?

It's a 2008 Ford Ranger

I was in an accident recently and one of the wheels has ceased to turn. It appears that the wheel "mount" (not sure if that is the correct term, its a rod with a ball on the end that attaches the wheel to the axle?) has come out of whatever it was in. The wheel and axle seem fine. How much would something like that cost to fix?

Is there any chance you could post a picture on here?
We can then have a better idea what you're looking at...