Mexico flights from the United States are fairly short (average 2 hours) and inexpensive. Today you can find Mexico flights by large carriers, from Canada and the UK, and small carriers in the United States. Most of the Mexico flights will go through Mexico City and some of the larger carriers will land in Cancun and larger Mexican Cities like Guadalajara.
Mexico has two large private national carriers:
Mexico charges an airport tax on all departures flights. Passengers leaving Mexico on international flights must pay $18 (US) or the peso equivalent when checking your ticket at the airport. This $18 tourism tax goes to Mexico's tourism promotional fund. Most travel agents will advise you of this tourism tax so that you are aware of if before reaching the airport. Many all-inclusive travel providers may even include this tax in your ticket price, but it is a good idea to check so that you aren't taken by surprise at the airport.