Buenos Aires is actually one of the cheapest, if not the cheapest, of all Latin American capitals. I haven't been there in a few years, but the difference between official and black market exchange rate alone made a massive difference.
I don't know how the exchange rate is these days, but back then you could rent a luxury 3 bedroom condo in Buenos Aires poshest neighbourhood for $1k a month or less.
Lima has both very good areas, where the cost of living is very high, and horrendous areas (most of the city, actually).
The only places I know in Latin America with a cost of living as high as Bogota are Sao Paulo and Rio. So I'm astonished to hear Buenos Aires is in that range now, since the last time I was around there the cost of living was easily half of what you see in Brazil and Colombia.
bogota i much cheaper than rio and sao paulo and rio and sao paulo are not as expensive as they used to be since brazil was hit hard by recession
Have prices in Argentina, converted to dollars actually increased?
I was also in Santa Cruz earlier this year, it's not really comparable to any of the major cities in Latin America, of course it is cheaper, but you get what you pay for.