hi, and welcome!!!
i would say that if the car is machanically sound and your only apparent problem is the cluster then you are in good shape. you can get the cluster repalced from the dealer for about $500 or
DIY (scroll down to cluster replacement) like this guy and spend about $300. try to talk him down using the cluster replacement to your advantage.
the clusters go out in
a lot of audis, so you may actually have a hard time finding a used one with it all (cluster and machanics) in tact. but if you repace it i think it would work well for quite some time.
don't forget to post pic in the "a6 soundoff" thread when you get it.[8D]