In addition to the Samba Parade , and all the fun in the Streets , Rio offers a selection of Carnival balls you really cannot miss. You won't have to spend a fortune to have a great time. If you are coming with a group, you can reserve a table, or even a box. While tickets for the Sambodrome should be reserved as early as possible, you do not need to buy tickets for Carnival balls in advance.
Tickets are for sale at the box office of most clubs and venues.
Call for box office hours, and purchase your ticket a couple of days in advance if that makes you feel safer. Costumes are not mandatory, with the exception of few balls. Putting on something special will help you get in the right mood, though. If you are traveling with a group, coordinated costumes are a lot of fun. A local probably could get away with it, but chances are you will dehydrate to death in 10 seconds when you hit the dance floor.