Here, I've made a table of exactly how much each portion of the trip cost me. My trip involved a mix of camping, hotels and staying with friends we met along the way.
The expenses listed include everything I spent, including souvenirs, personal goods and the occasional bus trip, although I tried to mention in the comments anything that might have affected the total cost.
I hope you can find this helpful at least as a guide.

Portion of Trip	Days	Cost per day (Canadian Dollars)	Comments
Argentine Tierra del Fuego	13	$25.42	Lots of camping, much free
Southern Chile (Chilean Tierra del Fuego to Puerto Natales)	21	$22.55	Lots of camping, much free
Argentine Patagonia (El Calafate to Perito Moreno)	23	$18.90	Lots of camping, plus we paid for a bus ride
Carretera Austral (Chile Chico to Puerto Montt)	22	$26.92	We paid for a few busses here
Central Argentina (Bariloche to Buenos Aires)	46	$17.63	We stayed for free in Buenos Aires
Uruguay	22	$10.44	Because of friends we stayed with, I only paid for accomodation twice in Uruguay. We also took a couple of busses. $10 bucks would be quite unrealistic otherwise.
Misiones (Argentina)	14	$17.12	Also includes a day in Foz do Iguacu, Brazil
Paraguay	7	$14.98	We stayed with a friend in Asuncion, otherwise we stayed in hotels
Bolivia	25	$15.54	Mostly stayed in hotels
Peru	35	$27.43	This is inflated by all my Christmas shopping (lots of souvenirs). Otherwise, Peru is pretty inexpensive. My figures don't include the Inca Trail (very expensive!).
Brazil (Manaus to Venezuelan border)	18	$27.88	Stayed almost exclusively in hotels, includes a 5-day boat trip down Amazon River ($200)
Venezuela	25	$39.99	Stayed only in hotels