Mines are currently at Ben @ BG Motorsport, There is a few reasons i went with them over cornering force even tho cornering force are slightly cheaper and with BG being the only official / Authorised sachs dealer made it an easy choice as all parts need to come from BG regardless.
My Refurb is costing me just under £900 but i am getting extra stuff done and getting the Twingo R1 Dust scrapers drilled in and fitted also.
Im sure a general service from BG is around the £500 with some postage costs onto that also.
BG have the exact same Powder matched to the OE colour and offer a fully powder coating service with new stickers add also.
As said cornering force is slightly cheaper and offer a good service also but i have read some topics on the fact that simon from cornering force is hard to get hold of and i know of 3 different people who have had there dampers fail within 6 months of being done there BUT saying that they where fixed and sorted FOC by cornering force.
Have a read of the last few pages (74 to 75) on the Trophy Forum.
http://www.cliotrophy.co.uk/forum/showthread.php/46019-SACHS-DAMPERS-REBUILDS/page74