Why prices of the posadas in Los Roques are higher than in other regions of Venezuela?

Mainly, because the logistics of transporting supplies to Los Roques is also expensive. There are only a couple of ships that caters to Los Roques and is common to hear from the people that works at the posadas that failed to fit into the next boat trip to transport their groceries or some of them were "lost on the way."

While there are stores to buy some supplies, prices are too high, for example, the cost of a bottle of water or gatorade is almost twice the price than in Caracas.