General Advice
Jobs
Chile/Argentina
If you don’t have the luxury of having a friend to tell you all there is to know about the cost of living in Chile, I would go on Craigslist and apply to some jobs on there (they’re probably going to be mostly teaching English, call centers, or bartending). Try to get as much information out of them as you can as for pay and frequency, and drop them. You’re just doing it to get an idea of your future income.
From my experience in Argentina, most of the expats found jobs through Craigslist (but it’s only for the main cities), friends, or native roommates. If you have some sort of English teaching certification (TESOL, TEFL, etc.) or are interested in earning one abroad, it might be a better bet for finding a job.
For a country like Argentina, which is poorer than Chile, the main problems I found with finding private tutoring jobs through Craigslist were payment, frequency, and need. In Buenos Aires I found an English speaking call center job and a cocktail server job almost immediately, but they each paid less than $3 per hour and kept horrible hours. The English teaching jobs I found through Craigslist paid around $8.75 per hour but were one hour only once a week. It might take you awhile to find enough of these private teaching jobs to sustain you while you’re over there.
Housing
Email hostels in areas you want to live and say that you stayed there last year (even if you didn't). Write that you liked the area so much that you’re looking to live there, and ask if they could recommend any apartment-finding websites to you. I once called a hostel I only visited but didn’t stay in, from the middle of a bus station and asked them to give me the names and numbers of local food delivery places (they gave me 3). Hostel workers are usually bored and are on the computer, trained to give people the most info about anything they’re asked. Use them.
Argentina
Before I left for Argentina the last time, I was able to find a site called Compartodepto, which is like Roommates.com for Argentina. This website made a big difference because to stay someplace in Argentina you either had to live (and possibly work) in a hostel, get a really expensive apartment through Craigslist (think Los Angeles prices for Buenos Aires: US$600 minimum for an ok neighborhood), or sign a 2-year lease for an apartment at inflated foreigner prices.
Before I came to Argentina I booked a hostel in Buenos Aires for week so I’d have enough time to look at apartments after school (registration was the day after I landed). I looked at four apartments and got a place in 5 days. If you stay at a hostel, you have the added benefit of having the workers there give you advice on the good neighborhoods or websites to find apartments or furniture.