Every items they sell in Oxxo are more expensive than in the supermarket or in a small independent store, so, whenever you want to save some money, don't buy in Oxxo or similar convenience stores.
@Ssabukim by the time you become fluent in Spanish, a lot of more options will be availablefor you (as it happens with every language), here in Mexico we love to help people and give our best advice, so you can technically ask any random people for advice, lets say, the cheapest, safest place where you can buy food, gadgets, Sim card, etc. They will even offer to accompany in order to guide you correctly; that been said, if I can help you from the distance with anything, please just reply to this message and I'll be glad to help...
