First off, if you're leaving in 2.5 weeks it's almost certainly a little late in the game to be thinking about vaccinations. Typically you'll need to get those done (sometimes in stages) at least a month if not more in advance, except maybe for the Typhoid pill if you go that route. Also keep in mind that vaccinations are quite likely to make you feel like shit for a while... but that's totally subjective for each person.
BUT: I haven't been to S. America but I have been to India 3 times (soon to be 4) and I'll let you in on a little secret...
I did not get any vaccines. And aside from the first trip, I did not take any malaria meds. I did not get sick, and I did not get malaria. (knock on wood for the next few times)
Feel free to go ahead and tell me how stupid you think I'm being but I'm sorry, I didn't have the $$$$ for rounds and rounds of vaccinations that are not entirely 100% proven to protect you (read up on them) and almost certainly make you feel crappy regardless.
On my last 2 trips I didn't take malaria meds because I decided that millions (MILLIONS!!) of people live their daily lives without them, and only a tiny fraction of people contract malaria. THAT SAID, malaria is absolutely not something I would want to fuck with, so it's a gamble. (This is why I take mosquito repellant.) But what made me decide not to take malaria meds was this: Doxycycline, the affordable malaria medication, is an antibiotic. Who wants to take antibiotics unless you absolutely have to? And Malarone is ABSOLUTELY NOT CHEAP despite what sleepisthecousinofdeath says (sorry, but it's just not. Unless you're Canadian or British maybe.) I did take Malarone on my first trip because I got some second-hand from a doctor friend who had just come back from Madagascar and had extra. HE PAID ALMOST $5 PER PILL FOR IT HIMSELF. Also Malarone needs to be started exactly 7 days before your trip to malaria-prone regions begins and needs to extend for 7 days after, so you have to buy 2 more weeks than your trip duration. FYI. Also, Malaria medication is a prophylactic and as such it does not prevent Malaria 100%. Generally speaking you absolutely can still contract Malaria, what the pills do is they lessen the symptoms and duration to a certain extent.
So, if that wasn't enough, the other reason I decided to go with mosquito protection instead of malaria medication is that Dengue Fever and Chikungunya are two very common mosquito-borne illnesses (in India anyway--I honestly don't know about S. America) for which there is NO protection and NO cure. So, I could choose to wreck my digestion from Doxy, lose a bunch of money from Malarone and
still contract one of those two. Yes, I know, Malaria still sucks... which is why I'm just telling you this as my personal opinion, not a treatise on what is exactly right for you. It's cheesy but your mileage may vary.
Believe me, I've done a lot of research on this (I may end up living in India at a certain point). I hope this helps.