Brazil practices the so-called "reciprocity" policy in terms of visa requirements. So, as the US requires visas for Brazilians visiting the US, so does the opposite. Please give yourself at least 10 days to receive your visa.  In most areas of the U.S., the Brazilian Consulate does not accept mailed applications*.  The fee for U.S. Citizens as of 2014 is $160.  U.S. Citizens also need to have a passport photo attached to the application.

*According to the Web site, Consulate General of Brazil in Chicago , Mail applications may be taken but there are restrictions

1. You must live in one of the following states:IL,IN,IA,MI,MN,MO,NE,ND,SD,WI

2. The Consulate accepts ONLY express mail envelopes carried by the U.S. Postal Service - U.S.P.S.  Envelopes submitted by other carriers will be returned without opening. 

The most accurate and up to date information always comes from the embassy. For US citizens traveling to Brazil, please refer there.