Hi,
I got the kit from ebay, it was about 75 quid delivered, the ebay company i think is vwteesside,
http://vwgolfr32.co.uk/shop/Retrofit-Cruise-Control.htm is the link for it, you can also find the fitting guide on this page near the bottom.
As for fitting the kit, it is not too difficult, the hardest bit for me was disconnecting the ecu plug, i have never done that bit before but luckily i know an audi tech who helped me out.
Basically it is mostly running wires into connectors, however you do need a special bit to remove the steering wheel from the column, i think it is called a XZN socket or bit, it is splined but not the same as torx etc, i got a set from the local autosave for a few quid.