If cost go up with current rates in 2008 it will probally be somewhere around 6000 peso a month.
If you do some travelling(some of Cordoba, Rosario, Igazu, Salta, Bariloche, skiing, week at the beach, Montevideo, Colonia, Peninsula Valdez, Perito Moreno, Santiago, Mendoza) it probally adds up another 100 dollar a month.