We found Rio to be a very inexpensive location. The US dollar was strong against the Brazilian Real. In May 2016 the exchange was approximately $.35 = R$1.00 or $35 = R$100.
Whenever traveling abroad, ensure your credit card company is aware of your travel dates and destination. This is typically an easy phone call to the issuing bank or even an online for completed on the bank website. I suggest only using a credit card vs. a debit card when traveling abroad in case of any theft or compromise of your debit card. If compromised, a debit card can allow your related bank account to be completely and immediately drained to a zero balance. A credit card will tend to be a safer alternative as you likely have a higher credit limit than cash in an account and if the card is stolen, your responsibility for the fraudulent charges are not immediately taken from your account or even held against your credit limit.
Specifically, in Brazil, it is recommended you avoid automatic teller machines (ATM) in any location except within the lobby of a bank. This is especially true of ATMs found in the airport or subway stations! There are instances of poor security in these other locations. Banks are plentiful around the city and have exceptional security in the lobby from multiple security cameras, heavy doors and walls of glass for easy visibility. They also have an extraordinary number of ATMs in each lobby. Much different than a U.S. bank lobby with one or two machines. These banks typically have 8-10, possibly 15 machines in a single, LARGE lobby. We also found bank lobbies to have opening hours posted, typically closing at midnight and opening early each morning, often 4am.
As a matter of course, I would suggest not taking a risk with an unknown bank but rather choose a bank known internationally, for instance HSBC.
I was concerned about arriving into a country and being unable to exchange money, remove cash from an airport ATM upon arrival, locate an acceptable bank ATM, etc. We were able to use a currency exchange in Houston during our layover to ensure we had cash when arriving in case of any immediate need, tips, etc. Most hotels are able to break larger bills you receive through a currency exchange or ATM withdrawal.
Your travel funds are valuable! Be Safe! Be Careful!