I’m Argentinian and have lived in Buenos Aires for a year.
Price-wise, Buenos Aires is quite expensive for Argentinian standards, specially rental prices. You won’t have a problem finding a place quickly, though. There is lots of so called “alquileres temporarios” that are basically fully setup flats you can move into without much fuzz.
Here is a Website with short term rentals, as above:
In terms of food and other essentials, prices fluctuate greatly based on which part of the city you live in (by as much as a factor of 4!), but you can expect to eat at a decent restaurant for 150-200 ARS and most fruits and vegetables can be bought inexpensively at your local groceries shop. Most other things you’ll want to get on one of the supermarket chains at reasonable (less than the US, more than most of South America) prices.
Anything imported (and I do mean, anything) is generally a lot more expensive than if bought overseas due to very tight import restrictions and high import duties (50%!). So bring all your tech and fancy make-up with you .
Argentina presently has tight currency exchange controls and the government artificially sets the price of the ARS to suit its needs. There is a parallel black market for the US dollar that prices it quite differently. At the moment, if you were to bring and exchange 1000 USD in cash in the black market, you’d get 14520 ARS versus 9590 ARS if you used an ATM or a brick and mortar forex shop. This essentially makes your trip a good 50% cheaper if you bring cash with you.
As for safety, I wouldn’t say Buenos Aires is the safest of places, but so long as you exercise common sense and don’t walk around laptop in hand at 2 am…
The Internet in public places isn’t the fastest and 3G operators have abysmal service (country-wide). Your best bet is finding a good coffee shop (certain Starbucks locations during off-peak hours, for instance) or one of the co-working spaces in town. I haven’t personally used the latter so I can’t comment on those, but I’ve heard good things.
Transportation is ridiculously cheap. I was there a few months ago with my girlfriend and I think we spent around 6-8 USD each over the course of a week. No taxis.
In terms of entertainment, the city is pretty damn big and culturally diverse and there is always something going on for everyone: football matches, theater (featuring world-class acoustics on one of them), endless bookstores (one of them is a converted theater!), all kinds of random events (randomly bumped into a German/Austrian bratwurst festival last time I was there), second-hand arts and crafts markets on the weekend, etc.
Hope that helps.