To estimate the price of the 2015 Mercedes GL500 V8 4.7L Twin Turbo with 204000 km mileage in average condition, I first considered the selling price of a similar car: a 2015 Mercedes GL500 V8 4.6L with 96000 km sold for SAR 135000 in December 2023. Given the higher mileage and average condition of the target car, a significant depreciation is expected. Next, I looked at listed prices of similar cars. A 2015 GL500 V8 4.7L with 207500 km was listed for SAR 77000, and a 2014 GL500 V8 4.7L with 218000 km was listed for SAR 63000. These listings suggest a lower market value for high-mileage cars. Considering the average condition and higher mileage of the target car, I estimated its market price to be slightly lower than these listings.