Is there a cost involved in setting up a codeshare agreement?
 

Just wondering why some airlines only codeshare on select routes, not all routes covered by each other. Eg. Was looking for ORD-COK (Cochin, India) through AA.com and could not find an AA codeshare on 9W, then realized that their agreement did not have one. So is there a cost involved which is why AA did not want COK as they don't expect many bookings to COK?