As of March 1, 2015, Argentina has doubled the fee for overstaying your tourist visa for non-Mercosur residents from $300 pesos to $600 pesos. This also applies to extending your tourist visa by 90-days.
Considering that it was last changed almost 6 years ago, this was long overdue, and with the rate of inflation here, it’s still quite a bargain. In 2009, the fee was sextupled from $50 to $300, so doubling is almost nothing. Looking at this in dollar prices, the $300 fee in 2009 equated to U$S 81 while $600 pesos in 2015 equates to U$S 47 on the blue market.
You can pay this overstay fee at Ezeiza, Aeroparque and the Retiro bus terminal, but for other ports of exit you must pay the fee online in advance.