Play in steering wheel is greatest when travelling 50 mph or faster

There's two things to consider. First, Ford has a lot more trouble with steering and suspension parts separating leading to loss of control and crashes than all other manufacturers, so besides ball joints, have those systems inspected at least once per year. Worn parts are not as common on your car as they are on Ford's front-wheel-drive cars. We don't get involved with costs here because there's way too many variables. As a generalization, it typically takes about an hour to replace one pressed-in ball joint, and a little less than double that for both ball joints on the same side. The car should be aligned after that service.

With worn parts, you may be able to observe the front wheels as you move the steering wheel a small amount. The wheels should start to turn as soon as you turn the steering wheel. If you can turn the steering wheel more than a couple of inches before the wheels respond, suspect worn parts.

A "floating" sensation can also be caused by not enough "caster". That's one of the three main alignment angles. Caster has very little effect on tire wear but when it's unequal on both sides it will cause a pull toward the side with the lower setting. Caster also has a huge effect on steering wheel return after cornering. Higher caster provides more directional stability at higher speeds, but it makes the steering wheel harder to turn. We went to higher caster in the '60s when we started driving faster, but to make up for that harder steering, we added power steering.

If you look at the car from the side, positive caster means the upper ball joint is more to the rear of the car than the lower ball joint. Those are the two steering pivots. You can see the same thing by looking at how the fork of a motorcycle is tipped back on top. Caster will be lowered when the back of the car is raised up like we used to do decades ago. On Fords with air bag suspension, leaking air springs are common. If the front doesn't raise up to its proper ride height but the rear does, that will also lower the caster measurements and cause a light steering feel.