The Mondeo ones won't fit as they have a different shaped front plate and the radio itself is different dimensions.
If you go to Ford you'll be looking over £400.
TBH eBay is your best bet.
Mondeo radio, note the angled face plate and that it's wider at the top (as per arrows)
Focus radio, face plate is a regular rectangle (as per arrows)
One thing to be really cautious about is that some sellers list the radios incorrectly.
Don't instantly believe them when they say it will fit a Focus, look at the photo and gauge for yourself.