Roughly the cost to replace a coil on an outside unit/condenser should run about $400-$500, depending on the size of the unit and type of refrigerant.

Typically the Service Tech will replace the refrigerant, and possibly the liquid line drier.

Good luck!

It all depends which coil you are speaking of, Evaporator or condenser if you are lucky to find a used match which is highly unlikely. newer units have has their seer rating changed substansually causing both coils to be replced at the same time and by the time that is done a new lineset is required to elliminate cross contamination so its not good news depending on required tonage 3000 to 5000 dollars installed sorry wish it was better news