Embassies & Consulates
Paraguayan Consulate Paraguayan visas cost US$65 for most nationalities but US$160 for Americans at the time of research. Visa processing takes three hours, and you'll need your passport, two photos and a copy of your credit card.
Brazilian Consulate Visa processing (Australia/USA/other AR$2400/3600/1600) takes 24 to 72 hours so visit as soon as you arrive in town. Apply online first and print out the receipt before visiting the consulate with a bank statement, a photograph with a light background and a ticket out either from Brazil or Argentina.
There are various free wi-fi zones around town including in the Plaza San Martín.
Currency-exchange places are along Av Victoria Aguirre downtown. If you've got Brazilian reals, you're much better off changing them in Brazil or buying services with them here rather than changing at official rates.
Macro Has an ATM.