I have an S4 exhaust for an Avant sitting in my garage. I was going to retrofit it to my A4, but decided not to. With school and everything, I just can't afford it right now. I have pics at home that I will try to have uploaded today. Just come pick it up. Whoever gets to my house first can have it. lol Oh...there are some sort of tips welded on it. Don't know if it's stock or added. One more thing...The exhaust is a stock S4 exhaust. So, if you are needing to put your S4 back to stock, this would work for you.

http://www.freakyshiat.com/upload/pictures/S4exh3.JPG
http://www.freakyshiat.com/upload/pictures/S4exh2.JPG
http://www.freakyshiat.com/upload/pictures/S4exh3.JPG

how much and how much do you think it cost to retrofit?

Oh...I forgot this was still posted here. The exhaust is gone. Sorry. :(