The company that you mean are "Cool New" based in Romford.
Their website is
www.coolnew.co.uk and they are a sponsor of MINI2.
I think that £150 sounds pretty good, but you'd better sit down when you get the quote from the BMW garage !
Not many main dealers have their own bodyshops nowadays, but ship the work out to a preferred bodyshop.
A friend owns a bodyshop and does work for the local Volvo, Honda and Rover dealers.
As with any supplier, if the work isn't up to scratch (excuse the reference !) then don't pay until it is done correctly !
Best of luck.
Mark.