Some other costs to include that most people don't think about: airport parking or transportation fees if you're choosing different area airports or even different terminals within the same airport, additional food and beverage costs if an airline does not serve them to you, paid WiFi fees, and onboard entertainment (e.g. renting a movie to watch on the plane vs using the IFE system).
And always look at the first class pricing as well if the airline offers it, it can actually save money over flying coach if the perks work well for you. One money saving perk to consider besides the obvious (more bags and onboard food) is that you arrive rested after a long flight, which means you will frequently be able to immediately drive once you've landed, and that can reduce your airport transportation costs or increase convenience or both. Another benefit offered on some routes is meal service at the airport, so if you're taking a 10:30 PM to 7:00 AM flight from LAX to JFK, you can arrive at the airport a bit early, be fed dinner, and then have breakfast on arrival, saving at least $20 per person.
You're also more likely to have space in the overhead boarding first, and if you are prone to airsickness the front is less susceptible to turbulence and is quieter than the back of the aircraft. On the 717, MD-80/90, and some regional jets, the back where the engines are mounted can be deafening.