I would suggest watching some videos on YouTube. It's a sea of knowledge. Personally, I wouldn't go for a CNG car as the use on CNG tends to mess up the engine. Your air intake is also partly blocked to keep air level suitable for CNG so it does not work good on petrol and the suspension is also modded and raised which affects vehicle stability.
If I had to change cars I would spend Rs 800,000 on a 1998-2000 BMW 3-Series E46, get it thoroughly inspected, get the bad parts replaced with everything ordered from BMW Pakistan and Germany, and have a great car.
Still, Sunny has a much better drive than 2017 Corolla or Civic. You could negotiate it downwards to Rs 800,000 because the car already needs AC repairs and tire changing most likely. You could inspect the car for accidents using YouTube tutorials.
The trick to price negotiation is to find as many faults in the car as possible and use them to negotiate the price downward.
Simple Rule: Pay premium for good condition. Discount the price for faulty components.