To estimate the price of the 2018 Hyundai Elantra I4 2.0L Smart (Base) with 126000 km mileage and average condition, I considered several data points. First, I looked at the selling prices of similar cars. The closest match is a 2018 Hyundai Elantra I4 2.0L GLS (Top) with 80000 km sold for 50000 SAR on 2024-05-10. Given that the GLS (Top) variant is higher than the Smart (Base) and the mileage is lower, the price should be adjusted downwards. For older models, a 2016 Hyundai Elantra I4 2.0L Smart (Base) with 172000 km sold for 30000 SAR on 2024-01-20, and another 2016 model with 344500 km sold for 23500 SAR on 2023-09-10. Considering the age and mileage differences, these prices suggest a lower value for older models. Additionally, a 2017 Hyundai Elantra I4 1.6L Smart (Base) with 203000 km sold for 29000 SAR on 2024-06-25. For listed prices, a 2018 Hyundai Elantra I4 2.0L Smart (Base) with 126000 km is listed for 45500 SAR, and a 2018 Hyundai Elantra I4 1.6L Smart (Base) with 128000 km is listed for 39500 SAR. These listed prices are generally higher than actual selling prices. Considering all these factors, I adjusted the price to reflect the market conditions and the car's specifics.