Go and look for a reputable and honest mechanic, then ask them for an estimate of the general overhaul cost. IMO, It would be much better to replace the engine than do the overhaul if cost is almost the same.

Kia Pride's engine are a pain in the *ss if not treated properly especially if you are not the first owner. A surplus Japan Engine of the same models and a lot better in terms of durability and performance (B5/B6 SOHC) will stash your pocket at about 12K-15K, you can haggle the price to go a bit down. Only trouble with changing the engine is the papers (LTO change), but in the long run, a 1500 or 1600 SOHC fitted on a Kia Price will result in a better FC due to it's power to weight ratio.

Or if you have the moolah, go for a more bigger engine and EFI system (Z5/B6/BP). Most Kias that have changed their engines to EFI has an average of 14KM/L FC.

Trust me, I've been on that path.