Giving Horrible Mileage on Petrol
This leaves no point to waste money on petrol.
I think you should get the following setup;
Landi Renzo or Gaspetro CNG kit
PVR or Argenchip Lambada Controller
PVR, or Zetronnic Emulator and Advancer
A good Cylinder like ETC, Inflex of Kiyushi
Use Bosch 4 tip plugs for best results on CNG
Cost will be 50K or less, not more then that. But its Karachi, so i cannot confirm. I am sure about Islamabad.