Not really a tech question.
Too many variables to answer. Larger carriers buy fuel in the futures market, then trade it around, spot prices can vary all over the map but the majors can then lock in a price. Despite that, some locations are less expensive than others for a variety of standard economic regions, so airlines will carry more fuel from less expensive locations (even though the aircraft burns about 10% of that in just carrying it), etc. Aircraft are rarely "filled up" with fuel, only enough fuel is carried to meet legal and "pilot comfort" requirements due to the limitations on payload and the cost of carrying it. How much to fill up and aircraft would also depend on what the starting point was and even the customer configuration for the aircraft.