The cost of food in airports differs from airport to airport.
In LA Airport, I managed to buy a small soup (of decent size) plus a small bag of chips for about USD$5.
In Detroit airport, I purchased 6 nuggets for USD$3.25 (including taxes) from Popeyes (fast food chain).
In Toronto, Canada – Pearson International Airport, I had a Turkey roll, chicken noodle soup, iced coffee and a cinnamon roll for CAD$10.29 (including taxes).
At Nadi, Fiji airport $10 got me 2 pieces of toast, 1 large bag of Twisties (cheese chip like snacks, made Halal in Fiji!) and a small bottle of juice for USD$10. There only seemed to be 2 places to buy food at the airport, one in the middle and a small cafe near the back left.
Fiji bottled water is the cheapest drink you can buy and there didn’t seem to be any water fountains.
This is what you can buy for USD$10 at Fiji airport at 6am: