Retro fit of factory fit parking sensors (Integrated into stereo)

Hi, just received my B8 A4 with the standard MMI (concert radio) and was wondering if it is possible to retro fit the factory parking system which is integrated into the stereo (stereo volume decreases when in use). If so what is the rough cost? I have found this: KUFATEC GmbH & Co. KG - APS Audi Parking System - Rear Retrofit - Audi A4 B8/8K 36053 but the description isnt exactly great.
Also £453 seems quite steep to me for a parking system when they are available for £20 from ebay, so I was wondering if there are any other benefits to the factory system?
Thanks
Nick.

Anyone???