I own an X reg audi s4 avant quattro, and i must say, it is soooo enjoyable to drive!!!   The reliability is fantastic, and parts are reasonably priced.  The previous owner had the car tuned with a custom re-map and a milltek exhaust, which gives the car around 340bhp.  I am a d.i.y mechanic and have found most jobs a doddle to do. (i have heard that most engine jobs..i.e exhaust, turbos etc, are a bit of a pain in the bum, and some jobs involve taking the entire engine out!!!), but as long as you keep ontop of the servicing, replace parts when they need replaced, and give the car regular visual checks both ontop and underneath, i can't see any reason why the car should give any problems.  I have owned many audis, mainly 80s, and a few a4s, but this is in a diferent leauge. i would definetly reccommend buying one.  Having some mechanical knowledge is an advantage, as these cars need to be "kept on top of" as mentioned earlier. Oh, and investing in an O.B.D code reader will help alot. My one has saved me hundreds of pounds. It's pretty basic, but does the job..tells you what faults are stored in any of the car's e.c.u.s, clears them, turns off engine light, a.b.s light, service lights etc etc. the list goes on. Anyway, all in all, a sports car at an affordable price, with good levels of comfort and very practical.  
Amount Paid (US$): 11000
Condition: Used
Model Year: 2000
Model and Options: s4 avant quattro 6 speed manual 2.7 bi-turbo