As with all mechanical things if they have been maintained over their life then high mileage shouldnt really be a problem. One of my 2.8's (Truck) is now at the 220k mark and that is used every day and does anything between 60 to 100 miles a day during the week and is in pretty good nick considering. The other one (O-no) is sat around 89k, and out of the two is actually the worst condition wise. The steering is now too tight (It was too loose and pretty much 'tacked' down the road. Having done it p too much I now need to loosen it off a bit) and I've had to patch it up with the welder too.
As for repair costs and the 2.8.... No more/no less than other vehicles tbh, they are simple beasts and have a minimum of electronics so theres a good saving there. The engine, being ISUZU is pretty much bullet proof, just keep doing oil/filter changes and you will be okay. Oh and a belt change say every 40k.
I have on Truck changed the turbo twice, once at around the 140 to 150k mark and then I used a s/h turbo which then failed about 50k miles later. Add the original mileage from the doner car which was around 95k to give a rough life of 145k I'm not complaining. It's now got a shiny new one (cost in the order of £520+/-) on it, well it was shiny new about 20k miles ago!
I've also put a new alternator on it, the last one passed away but then they don't like being stood under water or smothered in mud for any lengthy period. Summit to do with the electric stuff going through em so I'm led to believe. Leccy stuff confuses the ..... out of me so a new one went on and the old one is sat in the shed until I get round to fixing it.
This posting may have been helpfull, on the other hand probably not... Either way, I may have had drink when posting it in which case it's probably not as helpfull as it could have been
Work safe, and remember all technical problems can be resolved with a hammer, the trick is knowing where to hit it and how big a hammer to use (I often find it may also help to have a spare bit in the shed to replace the bit you have just mullered

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Work in Progress (or not as the case may be) I give you....
'O-no' the truck.Comments on 'O-no' the truck may be left
hereWork in Progress (or not as the case may be) I give you....
'Truck'Comments on 'Truck' the truck may be left
hereOwning a 2.8 is a hobby in it's self...