What's a fair price to pay to have the refrigerant drained from the a/c system?

 

Why on earth would you actually pay for that service? All you have to do is depress the valve and vent the refrigerant out. I mean unless you are a bloody tree hugger...in wich case you shouldn't be interested in anything performance oriented in the first place.

 

Where is the purge valve located?

 

Just vent from the high side AC line. Of course once you do it you will have NO AC at all until you recharge the system.