I wouldn't purchase a vehicle with 500K on the clock unless it has maintenance records. If it's the original engine, it's toast at that mileage.........no matter how you think it drives.

If it's the original transmission (damn near impossible), it's got two miles left until it $hits the bed. Even if it's been replaced at 250K, it still has two miles left..............

It's not worth $1500. without some knowledge of the engine and transmission.