Looking at the petrol engine - 1.25, 1.4 or the 1.6 Ford say 100k miles (or 10 years)...which I reckon is pushing it a bit!
Beware....if you are going to have a crack at it, the crankshaft pulley is NOT keyed to the crankshaft Found that out the bloody hard way! Locking kits are essential.
You are looking at around 3 hours labour plus the parts.....you dont need a water pump as that is driven by the alternator belt but you will need the tensioner.
No need to go to a Ford dealer! An independant garage up here would be around £175 labour.