If you travel to Brasil and carry cash US$ , Euros,or British Pounds, with you, you must not overpass 10.000 RS,otherwise you risk confiscation by the customs authorities or the different types of police.(unless you declare the total amount,but for myself I don't trust to fill any declaration like this,as a tourist in Brasil....)
Much better to be legal, and for finding out the real value of your US$ or Euros ,changed into reais (RS),you can access the site: http://www.xe.com/ucc/convert.cgi
you will have instant conversion of your currency into reais based on that day exchange,and know how much cash you can have on you...
Site which I found now and useful for all who travel to Brasil.