If you just want the calipers, which is all you need really, then buy them direct from the UK importer - GPR Direct. I know he's a mate of Ali on here and they've done some stuff for me in the past and always been top notch service.
Price for a P4 from them is £136.92 per side.
Really easy to swap them out, so if you need a hand let me know.
http://www.gprdirect.com/epages/GPRD...Catalog/1227/3