I'm Argentinian and live in Buenos Aires city.
YouŽll never expend less than U$S 100 per day, including hostel, food and beverages if want to have a trip and live like a person. Need to include de tickets (bus is not expensive, but 3.000 km of road are not for free...).
If you are in a low fat diet or like sleeping on the floor of bus stops, well....
The people of the region you are plannig to visit, leave of tourism
This region (Ushuaia, Calafate, Torres del Paine...) must be visited from December to March.
Note: Sorry about my english