Just picked up my new 208 last weekend and took the option of the rear spoiler it cost the total of £416.00, fully fitted colour coordinated and brake light inset.not bad from a main dealer. Be careful to get insurance quotes because it is classed as a modification and some would not quote.
There is a garage in Nuneaton selling genuine ones on ebay for 255 buy it now. That is the full kit. Coloured top, 3rd brake light with cable, water hose extension, base peice and all the screws, bolts and inserts to fit.
However I went to my dealer for a price and when they said £318 I mentioned I have found one online for 255 and gave him the item number to check it out. Anyhow he come back to me saying he can put 17.5 percent discount on which meant I got it for the same price. (Well 97p extra but worth paying to get it there and then.