The brown code is the workboat code. Is the vessel still coded to this or has it lapsed. If lapsed i believe that you will need to start again. There is anew harmonised code that embraces many of the previous separate codes - red, yellow, brown etc
An Advanced Commercial Endorsement (equivalent to Coastal Skipper) allows you to operate up to 20 Miles from a safe haven day or night - or less depending on what the craft is coded to.
Far more info is available here about the endorsment itself http://www.rya.org.uk/training/yacht...tentId=3721708
The cost is set by the RYA and is something like £120. Of course if you undertake additional training with a school ahead of a course then that is charged according to your arrangment with the school.
Hope this helps