Passenger wing mirror damage?

4yr old Ford Focus zetec 1.6 (not electric) The wing mirror has been damaged. Bought replacement glass, colour coded cover. The prob seems to be with the swivel mount that you fix the glass to. It has come out of the three prongs and won`t go back in for love nor money!! It looks broken. :( How much is it likely to cost me to fix of is there a slim chance I can do it myself??