It will depend on origin and destination. For example, a flight from Los Angeles to Mexico City will cost around US$500, while a flight from New York to Los Cabos will cost some US$670.
If you consider other countries, the cost increases. From say, London to Mexico City it will cost over US$1000 while a flight from New Dehli (India) to any place within Mexico will be above US$2000 per seat.
Using Orbitz, the cheapest plane ticket I found was one for American Airlines for $231.80, from Los Angeles to Albuquerque.
Go to travelocity
Your plane ticket and a passport.
$100
a plane ticket or gas
It would cost a little over £14000 there you go!
It depends where you go and which company you buy the tickets
kit would cost 246
Chile
No. If you enter Mexico by plane you need a valid passport. If you enter Mexico by land however, it will not be much of an issue; however on your way back to the US you will have to show at least an ID or birth certificate.
How much does it cost to go to Mexico?
2$ 1 british pounds