1. Can I get one in the budget.?
You can get 94-98 model but any model up 98 would cost you around million.
2. What will be maintenance expense.?
If engine and suspension is sound then regular oil/filter change not too much.
otherwise it's maintenance would be night mare
3. Will it it be good decision to buy such old car for daily drive.?
if you can get one in good condition which is mechanically perfect and able to run on CNG then that would an excellent decision.
4. Availability of part will be easy or difficult?
I guess this model is not too common in Pakistan but you can get Kabli parts easily but they must be very expensive.
5. Any other advice if you think necessary.
If you have no plans to drive on long routes then for daily use i would reckon some small car with CNG relatively newer model i.e coure or cultus.if interested in Sedan You should also consider 98-2000 xe and 98-2000 VTI oriel.
6. Let me know if any one is selling?
I'll ping you if i came to know