What might cause the loud, fast ticking noise from the engine area of my '0?

I have just bought this car. It sounded alright on the test drive, but when thoroughly warmed up loud fast ticking came from the alternator belt area. This faded at lower revs cruising at speed but was louder in lower gear and when idling was rather noticeable even without the bonnet up. Does this model have a cam belt and does it need replacing. Is this very expensive?