My TD5 ES has done 115k miles and has a complete history. It costs about £350 for a major service and £200 ish for a minor service. In my book, the Disco TD5 likes to be maintained and if you spot a minor issue, deal with it before it becomes a major one.
I cannot describe it as unreliable as it has only ever failed once with a faulty hose. Buy safely with a complete history and if worried, pay for a warranty.
If you drive 20,000 miles a year, budget £600 for additional maintenance.
The Disco looks better, drives better, tows better and stops better than the Ford and they represent good value for money.
Buy the newest one you can afford and check everything thoroughly including the rear air suspension (with doors shut).
Worthwhile upgrades are KN filter, PSI chip, exhaust and cross drilled and vented discs with uprated pads. - V8 like grunt with respectable fuel consumption.
Good luck with your search.