how much will front ball joint replacement be?

We don't get involved with repair costs here because there's way too many variables. Besides, we don't have any idea what is wrong. Ball joints rarely cause shaking in the front end. It's more common to have a broken belt in a tire, especially if you feel and see the steering wheel wobble left and right at low speeds as in a parking lot. If you only feel the shaking at highway speeds, suspect an out-of-balance tire. The place to start is with an inspection at a tire and alignment shop. Ford does have way more ball joint and steering trouble than any other brand, but an inspection will determine if the ball joints really are worn.