I have a Lancer 1993 Diesel and just a few days ago I took it to 180km/h on Motorway. (I know going to such speeds isn't advisable). And the car just went on without a problem.
And of course diesel engines last a lot longer than Petrol ones and definitely more than Petrol engines running on CNG.
You can get a good Lancer 1993 Diesel well below your budget. Parts are not expensive, as some people would have you believe, and parts last a long time.
You can get a brand new diesel engine for the same car from Peshawar for 35k (without negotiation and also keeping the old engine) or a Petrol engine for 25k with the diesel engine adjusted. (Prices may change depending on who you talk to and where).
I got my car from an Ad on this same site some time ago and I use the car for long travels.