Where should we travel?

My girlfriend and I are both 19. We're doing a 5 month externship for culinary school apart from each other. So at the end of september we want to celebrate the end of our extern by traveling somewhere. She thinks we're going to key west. But im thinking about surprising her. I want to take her somewhere in the western hemisphere that would be exotic, unique, but not dangerous. I was thinking about Brazil or somewhere in the Caribbean. Where would be an ideal vacation for us? Im looking to spend 3 grand at the most.