Too hard to say really mate, but ive seen them advertised for from as little as £14k upto say £20k. It all depends on spec and condition and until you look at a few, you never know if its 'worth' it.
I wouldnt be too bothered about a full ford history either mate. Just look for a decent history in general as many people actually see ford only history as a bad thing now.
You need to be having a look at AT LEAST half a dozen so you have a bench mark to work too and youll soon know when the right one pops up.
It depends how fussy you are too. £14k will not get you a mint one, in fact your looking very close to £20k if not more for a minter, with excellent ones going for £16k+ in my opinion. But i suppose it depends on how YOU judge 'average', 'excellent' and 'mint'.