The cheapest 4.2tdi on the auto trader at present is this 100k miler, with faults and minor impact damage at £15,500......
https://www.autotrader.co.uk/classif...01807168480556
Mine is 100% working, low mileage, full main dealer history, so hopefully I can find a buyer! I’m not in need of the cash to buy the Q7, but drive space and NCD is at a premium with too many cars