The Ford dealer is trying it on, if you were a private customer they should have given you an estimate for the work involved, as Kezo stated they were fully aware it was a Motability vehicle, it is there vehicle only they can authorise any work to the vehicle, you are merely a user.
When you say glove department, I am assuming you mean the glovebox, to gain access to the air-conditioning filter you press the retaining clips both sides of the glovebox, it drops down for access to remove and replace the filter, it a 10 minute job so why remove the dashboard.
My final point how do you know it was a coin behind the dashboard you only have their word for it, it could easily been there at the assembly line and recently dislodged.
After about 12 months all Ford vehicle start to rattle.
Unfortunately I have suffered a brain injury and occasionally I get confused and often say the wrong thing.