syngirl - thanks!
by the time I got in, paid reciprocity fee, went through immigration, it was already 10:15 or so. i decided not to mess with buses at this hour and go for a cab.
maybe it was due to the holiday, but none of the ATMs had money. so I asked the cab driver/coordinator if they would take dollars. he said no problem, then quoted me a price of what sounded like 130 pesos while charging $45. i tried to argue in my broken spanish that it's 4 pesos to a dollar and not 3, to no avail. so i walked out of the cab, went to the bank of argentina, exchanged my dollars, came back... and got charged 170 pesos. ugh.
your advice of taking MTL from aeroparque sounds like the best one. the ride to there from palermo is only a couple of miles, so total cost should be <70 pesos.