I'm Geroge. Thanks for using just answer. The other experts and I are working on your question.
First of all anything in a sealed system you will need an EPA Certified technician. If there is a leak by EPA regulations it will need to be repaired first before it is recharged with refrigerant.
As to the cost--It will vary depending on which part of the country you are and the cost of the refrigerant.
Labor wise I can only guess and I'm basing them on northern california. Usually $90 to $120.
Parts and materials Might be about $40.
Refrigerant depending on your type of system: R-12 now is $200 per pound.
R-134A is about $40 per pound.
Hope it helps