Come down with some cash and use the services of Western Union to top up as you need

Credit cards from outside the country use the official rate which is not good for the user

ATMs also use the official rate apart from the crazy charges - ok , I know some people get charges refunded but the rates are only good for the government.

The talk in the street is that the special virtual bank account mentioned by Gaucho100K will exchange at 180 to the dollar - But as he says the detail is nowhere to be seen and likely to be a hassle if you are on a 2 week vacation.