Depends who the Disco is for and what they want to use it for.
IMHO, early 300tdi models are the best ones, without the fancy electronics, but with more 'stuff' than the 200tdi. The automatics are a dream to drive (mind you, I'm basing that on having owned an old Saab 900 auto). Typically, a good (early) 300tdi will cost you £500 more than a decent (late) 200tdi, if you look around, so it is worth looking for.
High mileage shouldn't be a problem, as long as the car has been well looked after. Disco's, (as you probably know) have much more maintenance input than an average car, so look for one that has had full dealer service history.
Suspension, gearbox, alarm/immobiliser, leaking from the alpine windows and front windscreen, noisy turbo (no they are not supposed to make that noise!), rusty boot floor, general corrosion on the underbody (look for one that has been regularly wax-oiled), oil around the head gasket,
Remember that whilst the main body shell is aluminium, the roof is steel so can be prone to rust at the joins. Check the top sill area for damage (typically from roof racks) and rust. The front of the dash has a habit of lifting up, but that can be easily fixed with a kit. Inoperative dash lights are easily replaced. Rear washer jet normally loose, easily fixed. Central locking sometimes inoperative on some doors, again easily fixed.
Don't be alarmed if, when you take one out for a test drive, that the engine sounds noisy. Give it a 20 minute drive and make sure you get it up to 70mph; it''ll calm down.
Don't know about the leather. Some bits can be converted on the 200 to the 300 (lights, bumpers, but not engine), but you should be able to find that out with a bit more of an indepth search on this forum.
FYI, I have an absolutely beautiful '95 300tdi auto that I bought off Ebay for £2750. Came with air-con and the 'comfort' pack, and has most of the added extra's. It had 100,000 miles with 80,000 of those with full delear service history and was unmarked and no body corrosion. I still had to fork out for a head gasket and alternator replacement a few weeks into ownership, but them's the breaks!
