How much is a cylinder belt for a ford focus car?

If you mean a serpentine belt under $35.00 here is the serpentine belt diagram for a ford Focus

Do you mean the timing belt? If so, what year is your car and which size engine does it have?

Timing belts can be purchased for as little as $20, but most people also replace a few other components, like the tensioner, idler pully (if any), and water pump (depending on the car). Those items can add up to another $100-$300.

The labor cost to replace a timing belt is what makes it expensive. If the belt has broken, you may also need some serious engine work.