Tbh I dont think your budget is high enough. 7k might get you a B6 but it wont be a low mileage car. I looked at several before biting the bullet and scraping up a stack more cash for a decent RS4. The cheap ones are abused. Seems to me that the RS's get treated alot better than their 'S' brothers do.
Wohoo! picked up my B6 avant today and I'm in love already. 79k on a 53 plate, full history, needs a good clean but no rattles on cold start up and no clutch judder, fingers crossed.