2007 Ford Focus Air flow

We don't get involved with costs here because there's way too many variables, plus, we don't even know what needs to be repaired. Most likely you have vacuum-operated actuators and the vacuum hose feeding the system is broken or disconnected. Most heater systems are spring-loaded to go to the defrost mode when there's a vacuum problem. That's for safety. Your feet might freeze, but your windshield will be clear.