How much money will i need for my trip to South America?

Your question is too broad...

You truly would benefit from buying

some good Fodors guides and doing some basic research.

For me generally SA prices 50% or so less than US

if I am careful get by nicely $75 pppd...

No one can really answer such broad questions, as qwovadis says. A good guidebook would benefit you at this stage in your planning. I'll put in a plug for Fodor's since this is the Fodor's site: There's a South America guide, plus individual books for Peru, Chile, Argentina and Brazil.

qwovadis and Jeff_Costa_Rica are right that they are broad questions, but since I live in Buenos Aires I can tell you some of the prices so you can have a general idea.

A beer or mixed drink costs around $18 or $20 pesos

Lunch at a nice restaurant or café: due to our economic situation many of them prepare a standard menu which costs $30 or $40 pesos per person. They may include a drink (soda or water) and/or coffee.

A coffee costs no less than $6 or $7 pesos

I'm not used to eating in fancy restaurants so I can't help you with that or with the wine prices.
These sites might be useful, they are a guides about all kinds of restaurants in Buenos Aires www.guiaoleo.com.ar or www.restaurant.com.ar (they are in spanish)

At the moment $1 peso = USD 3.7, but this changes everyday

I hope this info is useful

In Peru, I found local restaurants for a simple lunch including bottled drink 9 soles to 13 soles ($3 to $4)

Tourist Restaurant you can double that.

Nice restaurant for dinner about 30 Soles ($10) main course but you can certainly spend more.

Pisco Sour about $5 US

Coffee less than $2 US

Thanks for the information. I know it was a broad question but the last two responses were very useful. I have done research both on the internet and through guide books, but I have found that nothing quite compares to talking to people who have been there which is why I asked. There seems to be plenty of information on the internet (restaurant websites) for places like Buenos Aires but its hard to know without having been there if these are the very top end or typical. Gleaning information on accomodation and travel is easy, but its the eating and drinking out thats more difficult.

Thanks again for your help and I'll make sure to be as specific as possible in future

Hi Michael.
heading to south america from dublin for 9 weeks myself. I plan on being home by the beginning of sept. Will send you a message at some point,give you a rough idea of how much I spent per day and what it covered, if you think that will be useful?
I haven't booked accomodation yet though, I plan on cheap and cheerful so it shouldn't add to my costs too much.

We spent 5 months in South America last year (Argentina, Peru, Uruguay and Chile) for two of us, we spent on average $100 per day all in. This covered staying in hostels/guesthouses with bath and occasionally in a nice hotel. Eating was a mixture of cooking in the accomodation (shopping at markets) eating out. We didn't stint on anything and stayed in some very nice places and some not so nice!
We are from England so one of the problems for us was the fall in value of sterling over the period an Italian couple we travelled with some of the time had the opposite experience, as teh euro strengthen v the $ over teh same period. It can make a huge difference to costs so you may wish to consider taking a mix of Euros and US$.

A couple of additional thoughts about Argentina...

Guia Oleo has an English version...scroll down to the bottom of the page and click on English. It is a very helpful web site.

A very good bottle of wine at an upscale parrilla in Buenos Aires will cost 60 to 90 pesos..many of the fixed price lunches mentioned above include a glass of house wine as an option...and a decent house wine costs less than 60 pesos. FWIW, there are some very good everyday or house wines in Argentina...so you do not have to spend a lot...