Having an auto shop or air conditioning technician add refrigerant to your car can cost from $100.00 to $280.00 depending on if it just needs topped off or it needs completely refilled.
If your car needs a complete refill of refrigerant then the cost would be around $280.00 to $300.00 because the system needs to be purged of air before adding refrigerant and check for leaks as well.
You can go to Walmart or auto parts stores and get a kit to refill the refrigerant yourself if you know what you're doing which is okay if the car just needs refrigerant topped off.
If the cars air conditioning system has completely leaked all the refrigerant out then it needs to be purged of air by a technician and then check for leaks and refill it to correct levels.