Fan belt noise on Iveco 75E15?

My horsebox has started making what sounds to me like a squeaky fan belt noise. It 'squeaks' until its warmed up, getting louder before it dissapears. Its in for some bodywork and Ive been told it may be a fan that is connected somehow to the crank and needs looking at urgently as it could take the engine with it???? It is going to the mechanic after the body work is done to be looked at but I wondered if anyone could tell me what they think and if this is a big and more importantly expensive job. It is a 94 cargo and I dont want to spend loads as Im considering swapping to a newer chassis. Many thanks