Old post on this subject here
Hello All, Does anyone know where I can get a key copied that doesn't cost the earth...?, I've looked at 'Timpsons' thinking they would be cheap..Owch: £300+ for a remote key copy. I'm based in Brighton, (South Coast). Peace. Baker
zroadster.org
Crux of the matter is you need a new blade cut and the key coded to the car, suggest you have a look on ebay for the key refurb services on thre that require you to post your working duff key to them, they can then cut the blade and use the transponder from the old key in the new one which would negate the need to code it to your car. You would have to sync the new key to the car for the central locking to work but that is done with a sequence of button presses on the key to sync it. Once you have synced the new key any other keys you have also require syncing immediately after completing the first one otherwise it won't work.
Other posts on the forum if you do a search for more info on key refurb/replacement and suncing the keys.
Local mobile locksmith would charge around £130 per key and may well want the EWS unit taken out of the car to code the replacement to the car using a new transponder.