Sorry to hear about this Shamus.
Super common issue.
Once the door is locked shut one of the only things you can do is bang the door with your fist as you lock/unlock repeatedly with the key fob. The hope is that it'll will open on one of your attempts.
I had this problem and no amount of banging and locking/unlocking would get it open.
I brought it to my local Auto electrician and he proposed pulling the trim off the interior door to get at the wiring loom for the lock and putting 24V across it from a truck battery, to literally blow the lock lock open!!
Not sure if this would of worked but he has solved a lot of electrical problems for me in the past so I have faith in his abilities.
Anyways, before we got as far as the 24V battery the door just randomly opened on one of our lock/unlock/bang the door attempts! So it's definitely worth persevering with that. Once the doors open replacing the lock is pretty straightforward.
However if you really, really can't get the door open you will sometimes need to cut the exterior door skin to get to the lock. Although this sounds absolutely shocking it's not that bad if you get a second hand door skin from a scrappers and fit it yourself.
The door skins themselves are very easy to take on an off (as long as you can get the door open that is!)
The most expensive part of the job would be getting the door colour coded to match. Unless of course you have the absolute luck of getting the right colour door skin from a scrappers!
Anyways.... Best of luck with it mate... hope all the above helps!
Regards,
Dave