Mexico's currency is the peso.
Paper currency comes in denominations of 20, 50, 100, 200, and 500 pesos.
Coins come in denominations of 1, 2, 5, and 10 pesos, and 20 and 50 centavos (100 centavos = 1 peso).
CREDIT CARDS AND ATMS
Visa and Mastercard are widely accepted throughout Baja California, with American Express being much less so. It's always a good idea to carry cash as well as cards, however, as smaller establishments are not guaranteed to accept credit or debit cards.
Travelers can easily find ATMs in cities, and they generally offer good exchange rates. Many larger establishments also accept USD cash, though you may not always get a fair rate so it's helpful to use pesos.