Doesn't sound like it's fitted. Speak to autologics as a few members have used them for retrofits.
I can't speak for the b9 but I know the retrofit on the A6 c5 requires a relay, wiring harness, mirrors with the correct motors built in & the updated mirror switch.
I suspect you'll need all this plus it being coded to the car.
Make sure the quattro system has been serviced if due. Also check tyres are the same on each axle and tread is the same level. As miss matched tyres or uneven tread wear can damage the quattro system.
I'm assuming its auto as such check to see if it's had a service. As the s tronic/dsg gearboxes can fail to change gears if oil is degraded.
Sound advice Steve but I don't think its what he wanted to hear, you know whats going to happen when the term cheap fix is mentioned, there are not any cheap fixes just cheaper.
Steve.