A small four-seat car usually costs around US$40 a day with unlimited kilometres; if you take the car for five days you may get sixth or seventh day at no extra cost. Requirements include being 25 years or older (21 with some firms including Avis), have a valid credit card in your name and driver’s licence (not just your IDP one). There is not much in the way of good deals though some of the more established companies like Avis have promotional rates – they are also less likely to keep charging your account, long after you’ve returned the car! It is also advised that you take out as much insurance as you can!
On that note it is advisable not to rent a car for Rio de Janeiro. As explained in Driving Tips below, driving in Rio and Brazil in general is too dangerous and fraught with inconvenience and costly repairs should the worst happen.