If you want to get around Bahia you can rent a simply car. The most international car rental are at the airport, but in the city you can find little car rental with special price, but you have to ask all the surcharge, insurance and more. For example the budget car haven't a illimited millage and the distance are very big so you finish your daily bonus in 5 minutes.
You don't need an international driving licence, but you need a credit card....
I prefer little car because are more 'invisible', normal simply car, but don't do off road ( like ride de sandy dunes or pass trou litlle river): Brasilian art special for it but you are not brasilian!!!!!!