Santiago will provide you with a low-key experience. The US$ doesn't go nearly as far as it did a few years ago, but it is still an affordable place. You can get into town in about 20 minutes to your hotel in a taxi/van. You don't want to stay in the "airport vicinity" because there is nothing out there, and with the new(ish) autopista, it is a quick ride into the city center. You can stay and go out in Providencia - Ave. Suecia has lots of clubs, etc., or a short walk (or cab) over to Bellavista at night for more clubs and good places (causal) to eat on the sidewalks, etc. I know people are going to tell you "go to BsAs (where I've been 4x and going back in late Dec) but I have to say that it is the one place I regretted going alone. I found that so much of the evening revolved around dinner (at 11pm) and so there was nothing to do from the time things closed in the evening until people went out to bars/clubs at about 2am.

ps - the little spanish you speak will leave you most confused in either Argentina or Chile, but you will tend to understand the chilenos a bit more. Chilenos are also (generally) more humble and friendly, but not nearly as good looking as the argentinos.