That's like saying: "Im looking to buy an older house....I know these things last forever and I'm just curous about how much it would cost if I decide to tear it down and rebuild on the spot?"
In other words - don't worry about it. You're asking the wrong questions.
When buying a high-mileage car, the right questions are more on the order of, "If I need a $2K clutch replacement or a $3K air conditioning repair, will I be able to afford it?"