sometimes when the cam belt snaps all the engines valve gear goes out of sync and causes lots more damage to the engine.
therefore by replacing the belt (which depending on the car and the garage that does it) can cost �100+ may not rectify the problem and you are still without a motor.
alternatively you could be lucky and find that the only prob is a snapped belt as the earlier reply suggests it depends on the value of the car and how much cash you have available.
baz