Have you been to Brazil? I spent almost 6 months there last year and completely fell in love with the country. I spent a lot of time in the northeast. It is far from the exciting hustle bustle of Rio and Sao Paulo, but it is such a special, exotic place. Beautiful beaches, fantastic music, and really interesting warm people. If you want more information about Brazil I will be happy to write you and let you know about my favorite places I visited.
Also if you want a cheaper tropical beach experience the Caribbean coast of Colombia is just gorgeous. Tickets to Bogota are not too expensive and domestic flights within Colombia are really cheap, like $50. Cartegena is a really fun city and to the east is Tyrona National Park which is stunning.
