I know it varies from country to country, but what's the approximate price on the things I mentioned above?
I am planning on backpacking through South America next year. I want to live cheaply and eat at local restaurants and spend the nights at hostels.
It is great that you are taking time to plan this. I have a good friend who is "slow traveling" through South America right now. Her rule of thumb is that she doesn't want to pay more the $10 USD for her lodging a night. By buying groceries and cooking in the hostel kitchen, so eats very well and very cheaply. That means that she doesn't have to watch every penny when she does go out to eat.
One thing you can do as you are planning is to log onto the airline websites and do a quick search of the trips you want to do. I always do that as I plan things for 2 reasons. 1. I get an idea of the price and 2. it lets me know if my route is easily doable or if I should alter my route to save time. Bus and train routes do the same.
I hope this helps a bit.
we agree with Brendan here that South America can be very inexpensive when you stay in hostels and cook all your meals (going out occasionally wont hurt you so bad either), we were able to cook a nice dinner for two with a bottle of red for less than 10$ and had some leftovers for lunch next day as well
The only things that hit your budget when traveling through SA are transportation and excursions. The bus ride (sometimes a very long one) can cost as little as 10$ and as much as 75$ for a secure bus line. The best way is to check what companies operate from/to the spots you want to visit and then check their websites for pricing:-) Sometimes it costs similar or the same (i.e. Brazil) to fly so check that option as well.
You should budget separately for excursions like Uyuni Salt Flats (around 160$), MachuPicchu (50$ entrance) or Inka Trail (have to book in advance and it costs around 500-600$ now), 3 day Amazon jungle lodge (120$) etc etc
we believe you need around 40$ a day to cover all expenses - we spent that much per person but we did not visit rather pricey Chile and Argentina:-)
Look into CouchSurfing as well - hosts in SA are amazing and it is easy to find a bed and have fun with locals:-)