Does the concessionaire pay a premium for the location? If so then some upcharge is inevitable.
Like with concessions at sport venues, concerts and other events that have a major amount of foot traffic you pay major bucks for the location and you have to do quite a bit of juggling to get your equipment into the tiny space.
You are also paying more for utilities, your shipping prices are up and you have to pay employees higher wages because of the drive and other expenses they have. You also have to have more employees because you can not risk having your place uncovered.
Once you got that set up you might be able to pull in some serious cash because you have a lot of foot traffic.
Of course it is like any business, you can price yourself out of the market. And people may just decide not to buy.
Your best items are coffee and fresh pastries with other hot food following.
You used to make money on people who would come in with the passengers waiting for the flight but that is mostly gone now.