A friend of mine has a Canon 24 - 70 / f2.8 lens that has been giving her some problems with focusing. She sent it to Canon for an estimate, and they said that the focus assembly and a 4-5th group lens assembly need to be replaced. Their estimated cost for repair is $750. The question is: is it worth repairing if it has that kind of a problem? Or should she just invest in a new lens (which runs for about $1700). She is a professional child / family photographer, so her lenses need to be in tip-top shape. If it is worth repairing, can anyone suggest an alternative to Canon (in the US) that might be able to repair the lens for less money?