Hi Steve well my boyfriend goes to Instituto uiversitario de lenguas modernas, he pays 180 dolares a month and he goes everyday an stay there for like 3 hours, he likes it and finds it very good. they have like 6 levels. in his classroom there's people fro every age group.
The price is the cheapest around and the teaching isn't bad, I was talking to an argentinia friend of mine and she was astound when she heard he pays only 180, other courses will cost around 450 dolars for the same amount of days and hours.
Well check it out anyway in the web and see what suits you best.
I am afraid I can't tell you much about the night life because I am looking to experience a bit of it myself... I live in Palermo and I heard there's good night life around here. Other places might be : Las Canitas and San Telmo
hope you found it useful.