I would go to a ford dealer anyway, or other person with the software to do the programming of ther master key, because SOMEONE has the keys to fit your car, this way you can have the old keys deleted, although they will open the locks, they then won't work the immobiliser as deleted.
Last time I had it done it cost me around £50 for one red master 1 black, bothe programmed, even the master as didn't have one, and all the old keys deleted.
tabetha