djniggle the twin 'sport exhaust' was a dealer fitted extra with the car and cost me £300. Not sure what it would be if bought separately I imagine abit more though, if they want £1000+ for the sx bodykit.
Heres a photo of the exhaust, only one I've got, not a great pic but you get the idea..
I think it suits the car quite well especially with the sx rear skirt trim. Although not too pleased with the movement of it, seems to wobble about quite abit under the rubber mount, and from behind doesn't look too clever, but need to get onto renault about that one!