I have a 2009 Chevy impala the driver side blows out heat but the passenger side blows out cold air what could be the problem and the cost to fix it

The selector switch is a combination vacuum/electrical switch. When you rotate the switch (with engine running) you should hear the vents open and close via a vacuum-actuator. The easiest thing to fix is the rotary selector ( Heat-AC-Def ... etc) about $50 on Ebay. The vacuum-actuator is a PITA to fix (it's under the dash and requires arm movements you did not think were possible) but the good news is it's only about $25. Or ... if your lucky ,,,,The vacuum line may have come of the vacuum-actuator ... it's possible but based on how difficult they are to get off the vacuum-actuator , I doubt that happened. You may have been fooled thinking it's the temperature setting (most people are) but that is only connected to a variable resistor