how expesive is it to sort out damp/ mould issue

[iWantChampagneOnColaBudget]

been looking at a 3 bed mid terrace and its second floor is riddled with damp.
ceilings, windows, walls are black with the stuff.

have asked a trader to have a look to get an idea of cost but wanted to have a figure in mind before he came round.

its a 3bed mid terrace pre fab house.
he did say ventilation would be an issue that needed solving as a main cause for damp

anyone??????

In most cases, you have the cost of opening the windows, and the cost of buying a washing line or a tumble drier, and the cost of buying an extractor fan for the bathroom.

Rarely there will be a water leak contributing to it.