From memory the front of the A4 has exactly the same control arm setup as my Passat, it's a total nightmare to work with / change and it's not a cheap job to do either.
Rear of the Quattro is fully independant irrc, so it's also going to be interesting to replace (price wise).
I did a full front end refresh at 90k, totally changed the cars feel on the road.
you look at the rear and then ROFL. the arms werent even straight and there were arms everywhere
cost wise id recon its the same as the front.
and then you have to consider rear diff mounts blah blah blah