The next time you're on an airplane, think about how much money you spent on your ticket — and then imagine how much the person next to you paid.

The prices might be wildly different. That's because plane ticket prices are "uniquely volatile," according to Scott Keyes, founder and CEO of Scott's Cheap Flights, a Portland, Ore.-based newsletter that sends daily airfare deals to 2 million-plus subscribers. Finding good prices, he says, has become an art form in and of itself.