I am currently in San Antonio and gave found:
Lunch in cafes:
From 4€ for an English style breakfast.
From about 5€ for a burger and chips.
From about 7€ for a pizza
(there are also Pizza hut, Burger king and KFC that are similarly priced to the uk)
Drinks in bars:
Non-clubs drinks are around 4-5€ but they usually do deals like a cocktail pitcher, 4 mixer drinks and 4 shots for 20€
In the big clubs:
Water 5€
Red bull 10€
alcopops 12€
mixers 15€
Alcohol from supermarkets:
This I found dirt cheap!
Alcopops (Smirnoff ice, WKD etc) are around 1.50€
1litre bottles of vodka/Malibu are around 15€
Gallon bottles of water:
usually come in 1.5L bottles and in a pack of 6.
A 6-pack costs from 3.90€ to 9€
but as far as I'm concerned, water is water and the 3.90€ pack is fine.