These have a somewhat common lift pump issue. When it goes bad, it'll starve the injector pump and make it hard to start, run poorly, etc. It will eventually wipe the injector pump, but not as quickly as the Cummins 5.9. Not sure what the lift pump costs, but I'm sure it's much less than the injector pump.
If it's the injector pump, it'll be dead, period. Plan on spending some cash at that point.
$1000 is a great price, $700 is even better if the seller is open to negotiation, but are you willing to gamble that on the ease of repairs? 75k on the odometer would tempt me to dig deeper. If the odo is original, it might be worth the risk.
Keep in mind, the 6.5's aren't the most enduring engines. They tend to get sold for structural failures (cracked block, webs, heads, starter block) more often than old age. When they're on, they make decent power, are economical at the fuel station, etc.
Good luck, let us know what you decide.
A thread I shared with someone else regarding the 6.5 this morning: Is the 6.5l a good engine? - Diesel Bombers