What you say is TRUE for an unfurnished apt. with GARANTIA, on a 2 year contract payable in pesos.... For a furnished place on a Temporary rental basis $600 will get you a room in a shared appt. maybe shared Bathroom
You can find a private room in a shared apartment for $400, but yeah for a furnished place to yourself, probably $700 minimum. Mine is about $800 a month currently.
Airbnb is a good place to look if you want piece of mind at the cost of being overcharged a bit.