As my S8 gearbox has failed I have been exploring different options of which the most likely is to partially dismantle it and sell some parts including cats and scrap the rest. Most places does not show the prices so I have completed couple of forms and expecting some quotes back, probably on Monday.
Below is the one that shows prices straight away on website
https://www.catalyticconverterrecycling.com/
Also a friend of mine is getting the price from his place where he sold his BMW 323 cat for £500 and 525 diesel cat for £100 when 323 got 4.4 transplant and 525 also had auto box failure.