Give rm cya £9k and walk away very happy. Nismo exhaust is about £1300 and is possibly one of the most sought after exhausts around, it's also got premium branded spacers and springs which finish off the look of the super light Ray's alloys and although you're not a fan, the Alezan leather was a £600 upgrade and IMO, looks amazing against a black car.
To answer your question, it depends on mileage etc, i've seen them go for about £8k, but then they'll have over average miles. Also seem them advertised for about £10 but take a long time to go because for another £1k you can get the 07+ version which has a nearly completely new engine with 309bhp, so about £9k for a well looked after one with good miles and service history is bang on, in my opinion of course.