SBJE:

The airport is only a few miles from downtown (about 25-30 min) -- a taxi should run around $23-25 US. Vast majority of drivers are honest, the vehicle can be a little "beat-up" at times -- one quirk is that the meters record "points" from which the fare is calculated using a chart.

If you're doing Iguazu-BA-Montevideo all in the same day, might at well fly. Your Iguazu flight will arrive at the downtown Aeroparque airport, from which there is service several times a day to Montevideo (Uruguay is the only international destination from this airport.) The miniature "international" sector at one end of the terminal building has all of 2 gates so it's almost never crowded. Air fare is somewhat higher than the ferry but not that much more -- Uruguayan PLUNA airlines offers some good deals as does the Argentine carrier SOL. The actual flight takes about 30 min, maybe a shade more with SOL who use SAAB prop-jets.