$62ea for (one) OEM TRW upper control arm (part only) Ebay has a pair for $119 - you can't replace just the ball joints on the Mark you have to replace the whole arm -either upper or lower. These are common weak points on the Mark. Not a bad job on the upper control arms -figure 4 hours for a first time do it yourself-er. Driver side is the harder, as the master cyl needs to be carefully removed out of the way to get to one of the nuts. I have not done lowers yet so cant comment, but from previous posts not a horrible task by any means.
I called a local Ford Dealer ( my Lincoln dealer sold out to Nissan) they wanted $550 + shop supplies and tax.
Oh and dont let this go it is dangerious - they can and will fall off and at speed can lead to trouble!!!!! Rich had this happen to his daughter.