Reprogramming the ECU could probably reduce the power consumption, but I don't think it's cost effective.

If you want a cheap, efficient car, I would recommend the Audi A2, which are dirt cheap, and you can get more than 25 km/l.

I have been looking around, and I have seen the A2 is not a popular car in South Africa, and only found this one.

https://www.usedcarsouthafrica.com/u...e/Audi_A2.html

Audi A2 1.4 TDI engine is the same used by the VW Lupo and Polo, so it should be quite easy to found parts if needed.