If it's simple like a Focus then £30, complicated stuff like the Grand Scenic where half the engine comes out or something then £60.
The cam belt itself costs more than £30

I just spend about £350 on my car, cambelt kit replacement, drop link, rear drums sorted out and handbrake tightened and a new tyre (nail in the outer part of the tyre, irreparable, had plenty of life left in it as well
). It'd be silly to scrap a 2004 car that only needed £300 spent on it.
What would even possess you to buy it in the first place? 
