To estimate the price of the 2012 Nissan Altima I4 2.5L S (Base) with 251000 km mileage in average condition, I first looked at the selling prices of similar cars. The closest match is the 2014 Nissan Altima S I4 2.5L with 242200 km sold for 31000 SAR on 2024-02-06. Another 2014 Altima S with 342000 km sold for 24500 SAR on 2024-05-30. Considering the 2012 model is older by 2 years, I applied a depreciation rate of 10% per year. This results in a 20% depreciation from the 2014 model prices. Adjusting the 31000 SAR price by 20% gives approximately 24800 SAR, and adjusting the 24500 SAR price by 20% gives approximately 19600 SAR. Next, I reviewed the listed prices of similar 2012 models. A 2012 Altima S with 251000 km is listed for 19500 SAR, and another with 289100 km is listed for 22500 SAR. These listings suggest a market range of 19500-22500 SAR. Considering the actual selling prices and the listed prices, I estimate the market price to be around 21000 SAR.