dunno, go in with something seriously low, say to the the seller i aint taking the piss, but it had a knock ( bumper ) and clearly aint been looked after (missing a servive ) its going to cost X amount at fords to get service, do brakes etc, even tho your doing it yourself.
say £5000 then meeting at £5750, then thats about £1000 to $1500 below decent market value, show the add for the blue one ect?
worth a try.
but as said there hundreds of focus to choose from.
personally i'd walk away