It seems most unlikely you would get a decent trade in from a NI garage. I looked up ford.co.uk on a similar mission and they set out all their dealers in NI. Alternatively, you could look up autotrader.co.uk - you need a uk postcode, try bt488pn - and you will find cars across the UK which will be cheaper than NI. Dealers in NI add on a couple of grand for the privilege of shipping the cars over. If you could sell your car here you will be in a better position.
Conversely, we have a 1.8tdci Galaxy and it averages about 43mpg, even fully loaded on holidays it only dropped to 42mpg, according to the trip computer.