When should a alternator belt be changed on a 2001 mondeo,and whats the cost.?

I have a squeaking noise when i start engine,once started the noise stops.I believe this is the alternator belt.The car has done 80 000 miles a serviced when it should be,and it is a 2ltr diesel,tdci engine thanks|||Replace the belt. The squeel indicates its worn.The mileage indicates its time for a new one.|||Don%26#039;t forget to inspect the Idler pully while you have the belt off. look for it to be hard to turn, feel rough when turned, or rock back and forth .