Hi Alex,
Having purchased a 2011 B8 A4 two days ago I have been researching options and come up with the following:
Gold £200 - £300 - All the bells and whistles: Install Apple Play Which will require something like this CarLinkit
Silver £95 Bluetooth connection and ability to use in car controls: Invery airdual bluetooth
Bronze £25 Blue tooth connection without use of in car controls: AMI MMI Adapter Bluetooth
I ended up pulling the trigger on the Bronze option last night, arrived today via amazon. It is plug and play, works well and automatically reconnects as as soon as you return to car. Apple play would be nice for Maps / Waze etc but it has a punchy price tag.
Thanks
Fraser