To estimate the price of the 2013 BMW 640 Gran Coupe I6 3.0L Twin Power Turbo Standard with 280000 km mileage, I first looked at the selling price of a similar car: a 2015 BMW 640 I6 3.0L Twin Power Turbo (M Kit) with 185000 km sold for SAR 66000 in April 2024. Given the older model year and higher mileage of the target car, I adjusted the price downwards. Next, I reviewed listed prices of similar cars: a 2013 BMW 640 Gran Coupe with the same mileage listed for SAR 56500, and other 2014-2015 models with lower mileage listed between SAR 60000 and SAR 83500. Considering the higher mileage and older model year of the target car, I further adjusted the price downwards from the listed prices. The final estimate takes into account the actual selling price, the listed prices, and the condition and mileage of the target car.