Sir there will be no monthly maintenance cost except service/cleaning/fuel in any good condition car irrespective if its a Cultus, Corolla, Vitz or Civic.
Vitz is a very good family car provided you can forgo the trunk space, full 5 persons seating capability for adults and can pay for the spares if someone has stolen the dash panel or side mirror assembly or if any motorcyclist has scratched the bumper or break rear lights.
Vitz is a very reliable car, parts are easily available in Karachi and they are far cheaper then 8th Gen Civic.
You can get an excellent Civic 05 EXI PROSMATEC for 950K Rs or a VTI PROSMATEC for 1050K.
Can also get an Altis Automatic 05 in your budget.