Unfortunately the Audi's suspension is a poor design and very poor quality. We do replace many of them. I'd say you are lucky if it lasted 6 years. Looks like your mechanic noticed the problem at the beginning and other expensive parts - like rack and pinion - could be saved.
Well, kind of expensive for the crap quality. There are 8 pcs all together, 2 upper and 2 lower on both sides, some of them are over $ 200/ each and there is labor also. Unfortunately this is the correct price for the OE parts. There are cheap aftermarket parts, but the quality is extremely bad, isn't worth the difference.