Chile and Bolivia - reasonable budget & how to get around

[deferry]

I just came back from my trip to France – best experience EVER!!!
I only stayed in a hostel once while I was in Marseille but sometimes it really made me smile, because all the clichés I read about on this site turned out to be SO true. And now ..ahh all I can think about is planning my next trip. I don’t know if this is kind of abnormal but actually that is the only thing that keeps me going right now. When I came back home the only thing I wanted to do is get back out there immediately. Do you ever have this feeling or is that just me?
Anyways…I got this friend in Chile and I’d like to visit her in February for about 6 weeks. I already searched for plane tickets but it seems impossible to get one under 938 € (~1243$)...cheapest one I found so far. Would it be smart to book as soon as possible or should I rather wait a couple of weeks?
I think I can stay at her place during my time there, have meals with the family and stuff but as far as my other expenses are concerned I really don’t know how to budget. My current plan is rather vague but roughly like that:
Week 1 & 2: travel around (Chile, maybe Argentina)
Week 3: Chile, stay at my friends place
Week 4 & 5: Bolivia (Salt Lake tour, see La Paz, Potosi, Sucre…I am open to suggestions, however!), maybe even add another week, depending on how I get along
Week 7: stay at my friends place (Santiago), then fly back home
As far as I have heard and read, Chile is rather expensive compared to the other South American countries but still cheaper than Europe for example. I have no precise idea how expensive it is to get around, once you are in the country, if somebody has any information on that – please share! I’d like to get along with 800-900$ while I am there but I guess this is rather tight if not impossible, considering the huge distances. I don’t mind sleeping in cheap, crowded hostels and buying food at the supermarket to keep the costs down, also talking slower, less comfortable buses/trains wouldn’t really be a problem.
Plus I am not that much into guided tours, so apart from the Salt Lake Tour, I'd rather try to do things on my own, which also might save me some money. 

[mooloo]

Unfortunately I can't help with most of your question, but I just wanted to add that I'm almost 100% certain that you will find it cheaper than Europe! I went to Argentina a couple of years back and it was very reasonably priced - we rented an apartment for a week (nothing flash but had everything we needed) for $210USD for the 7 nights. I know Chile is a bit different but Argentina would be closer in price than Europe I would imagine