$2.50 must be if you purchase it from a premium eatery, but at the grocery store they are $1, and often on sale for 79 cents.
There is a LIGHT version which has 0 calories that I enjoy. They are actually infused with certain vitamins and minerals, and probably a step up from soft drinks.
Whatever the cost is in Argentine, I am sure like most imported things, it will be so offensively expensive that I personally would not buy it. (Similar to the Blackberry Playbooks, which are currently on sale in the States for $199 USD since they havent had the reception REM was expecting, while being marketed as a hot new thing in BA for over 2000 pesos)
I found the marketing ads ¨Agua de Nueva York¨ to be hilarious. But Argetines DO love the allure of NYC and Miami so I guess this is a good plug.