Wa Alikum Salam Asif Bhai!
good advice from everyone and the point to emphasize once again is to buy one only after Pre Purchase inspection from a workshop that deals in SUV's. To get a good reliable and enjoyable vehicle, the shortcut is to be patient and be willing to pay a premium over market price. Another tip is to rent one from a reputed rental company preferably with a driver and take it to one of your upcoming trips upnorth and you will get an idea of what you are exactly getting into.
SUV's and especially the old ones cost alot to run, maintain and modify (i.e. making a camper). 3 Million should get you a decent hilux requiring less maintenance. Otherwise, maintenance and ancillary costs (lubes, parts, tires) can be high and will eat out of your monthly budget. Not 100% sure abt its mpg, but i doubt 2500cc would get you 10kms/liter but should be close. Do avoid the 1kd i.e. 3000cc in older hilux models.
Punjab tax rates can be checked here for a basic idea https://excise.punjab.gov.pk/motorvehicle_tax, taxes of ISB n other provinces are usually lower. If I am not mistaken, luxury tax is not paid annually and it is a one time tax which would have been paid by the previous owner.
feel free to ask any further questions n 4x4 enthusiasts would be happy to help