If you mean the auxilary jack that fits in the glovebox, I asked BMW about it. (If its not that, completely ignore all of this!

)
This is what they said:
"The Parts kit is £39.95 labour for us to fit is £148.02 - Total inc vat - 188.00
We'd like to bring your attention to the availability of retrofit Auxiliary Connection kits for MINI. With the increasing popularity of MP3 players and iPods a number of customers are enquiring about Auxiliary Connection points for these kinds of audio devices.
The Auxiliary Connection point is a connection jack for all external audio sources available on the market and is simple and quick to install (installation time is approximately 1.5 hours). The jack is installed in the glove compartment or oddments box.
The volume can be controlled via the standard radio controls or multifunction volume controls, however it is not possible to select tracks etc via the car's audio controls. The kit can be fitted to any MINI built after 09/02."
Hope zis helps!
