I believe you do NOT have to pay the reciprocity fee. I believe the reciprocity fee is currently only assessed for international arrivals into EZE (and, maybe, AEP). In March, I flew into SCL then took a bus to MDZ and them flew MDZ-AEP-FTE/FTE-AEP and I never had to pay the Argentina reciprocity fee or get a visa in advance (I'm a US passport holder).

There's a lot of info on the Destinations - South America - Argentina forum, like this thread: Reciprocity Fee for Americans at BA airports now $US 160

Also, this thread probably belongs in that forum.