If your unsure on the markup part you can see what the materials cost on ebay:

http://www.ebay.co.uk/itm/autoglym-lifeshi...SwWxNYogb2

Obviously here is labour to add for the application of the products but I think your approach of getting a detailer to prep your car will get you a much better finish. I stopped getting my RR washed at the LR dealers after watching my dashcam footage following my first service, never again ! 2021 P400 Silicon Silver AB
Gone 2011 Bournville TDV8 VSE
Gone 2008 Black Canadian HSE LUX