To estimate the price of the 2012 Kia Optima I4 2.0L GDI (Base) with 311000 km mileage, I reviewed the listed prices of similar cars. The closest match is a 2012 Kia Optima I4 2.0L GDI (Base) with 311000 km listed for SAR 25000. Another similar car, a 2012 Kia Optima I4 2.0L GDI (Base) with 256776 km, was listed for SAR 22000. Considering the higher mileage of the target car, I adjusted the price downwards. Other listings of different variants and years, such as a 2012 Kia Optima I4 2.0L T-GDI GT with 351000 km listed for SAR 28000, also support a lower price for the base variant. Therefore, I estimated the market price accordingly.