A8 4.2Q new cat is needed, where cheaply chew?

Hello, after my search for a catalyst for the
A8 4.2Q has remained unsuccessful, I hope now the right tips to
get where I can find it. For information at Audi, the right catalyst costs a lot of 1048€ and the left 865€ net
Not a little money, is it? Are the cats of the A6 4.2Q not the same as the A8 4.2Q? The new cats must of course think something and be cheaper than with Audi, because what Audi is asking for for the cats
impertinently expensive.
This is the facelift model from 2000 with 310hp
Hope someone has the solution for me
Thank you
Georg