any german main dealer can give you that price. i tryed to get them to do a group buy but they weren't interested in sponsoring the site. the standard kit comes with the 2 fins that cover up the holes. the spoilers in aspen silver can be got for less than £250, while white and black are around £250-£260, exchange rate dependent. woodmans bmw on this site are doing 310-340 delivered, can't remember the exact figure but in that ball park.
adhesive is usually extra -£25 from bmw.
contact details for the german dude i used (they're on ebay too):-
Autohaus Grötzinger GmbH
Siegfried Hopper
Teilevertriebsleiter
Im Brenntenstock 3
74613 Öhringen
Tel: +49 (7941)9434-40
Fax: +49 (7941)9434-34 emails:- Siegfried.Hopper@groetzinger.bmw-net.de
siegfried.hopper@autohaus-groetzinger.de http://www.autohaus-groetzinger.de
he charged me 324 euros (£260approx) including postage. that was for a black
jcw r53 spoiler with 2 fins to cover the extra 2 holes. the later spoilers are more expensive.
they occasionally have old stock that hasn't sold that they put on ebay from time to time, i've seen them go for <£200 so you could keep an eye out.
his english isn't amazing, but he is very straightforward and helpful.
here's another german selling one on ebay - note it's aspen silver so is cheaper than the quoted £260.
MINI One Cooper S JCW Carbon Spoiler John Cooper Works on eBay, also Heckspoiler -flügel, Spoiler, Auto-Tuning -Styling, Auto Motorrad Teile (end time 27-Jun-08 09:49:32 BST)
and another german...
eBay UK Shop - BMW: Original BMW, Radsatz, Komplett
they're good for
jcw wheels too, you can get up to £400 off the price you'd pay over here but still expensive though!