the stock engine is 1200 cc and is very light according to the weight of car. if u want both power and economy, then u can swap D15B3 Double VTec engine. it has 3 stage vtec system, means three separate cam profiles. when u r driving in normal conditions, stage-1 vtec is working. but when u need sum extra power to accelerate, then stage-2 vtec starts. in normal stage-1 vtec driving conditions, the fuel average will be about 13 to 14 km/ltr. and on highway cruising, it will go to about 18 km/ltr.
now come to the cost. i live in karachi and i know the prices of the local market.... from here. it will cost u around 60k. this amount includes engine, gear box, ecu, complete wiring harness, installation of engine in ur car, installation of electric fuel pump in ur car's gas tank. i mean complete setup will cost u around 65k here in khi.