VW polo door lock came out . Help.?

I have a VW polo 2003 and the door lock on the passenger's side has come out. Basically every time I insert the key and when I remove the key the lock (with the metal thing) comes out with the key leaving a hole behind. The lock is fully functional and does lock up as it should but but the metal thing with the keyhole on the side comes out. I tried super-glueing it but it didint work. Is this a major repair work and how much will it cost approx ? thanks