how difficult and how much it cost to convert pushing door for opening to pulling?

Commercial building codes require entry/exit doors to open to the outside by pushing. Residential doors and hotel/motel room doors open to the outside by pulling - helps the resident inside to barricade the door against intruders.

It can be done by taking the door & frame out and flipping the installation it so that the door opens in the opposite direction. Another way is to remove the door only, reverse the hinges and place the door stops on the other side of the door. The door stopsre narrow wood strips that prevent the door from closing beyond the door latch and hinge limits. You'll also have to flip the door latch bolt.

Hi this might depend on where this door is fitted. building regulations have a lot to do with most door openings in public domain.

Depends where it is. If it is somewhere easily accessible to the public, building codes require the door to open one way - outwards. This is for safety reasons.

As you've asked this in the car section, on a car it's not possible