going the independent garage route, as I reckon it should take ball park an hour to replace at a guess. Of course you have to factor in the Main Dealer, Eloys additive top up and ECU reset. And if your doing a lot of miles, with the saving on fuel and road tax you will make over six years of it's life time, it can be considered relatively cheap.
For a Focus 1.6 they can be had for [url="http://www.clickcarparts.co.uk/p/diesel_particulate_filters~13/"]£260 delivered[/url]
And going by that website if you opt to buy a 2008 onwards 2.0lt model, they are like Volvo S40's [they share the same engine] fitted with the newer filter that does not need replacing at 75K, nor does it require the Eloys additive top up every 37.5k miles.
Why Ford don't use the newer non replaceable filter on the Focus, is a question only Ford can answer......the tight gits
Then that would only leave the Dual Mass Flywheel to worry about