Very expensive route but without knowing the instructor and thier mindset about training it is hard to judge. They may be very good or just taking advantage of your inexperience....One of the centers told me I should take the PADI Scuba Diver first in order to get certified down to 12 meters (cost is $392) and once this is done then should take the PADI Open Water Diver to get certified down to 18 meters ($300).
This course is all you need to get certified to dive. But again, I don't know the instructor or how and what they teach....The other center said that since I felt completely confortable during the minicourse I should take the OW course directly ($320).
Ask around, visit local dive sites and start asking other local divers for personal recommendations.
Post a question in the South America forum for local shop/instructor referals.