OXXO is just up the street 5min and not to over priced that's where I get my MT Dew and chips if I don't run to Walmart.
They do stock Redbull, but they charge $5 for it, well they used to. I'm guessing they still do. I have been known to buy a few, they really help when I'm flagging. Not sure about Monster. I would imagine the store over the road will sell it, or there's Starbucks. The mega coffee with 2 extra shots would have the same effect!
My wife brings her own 12 pack of red bull, to avoid having to pay down there. I have in the past brought about 8 Monters to mix with Jagermister. Across the street they do sell mosters, but they only had the regular (green can), I like the no carb (blue can), so it was a safer bet to just bring them. Not 100% sure if they had them or not.