I'm not familiar with that agency you mentioned but a co-worker who's pretty familiar with a lot of these places recommended
http://www.ojopropiedades.com/site/home_eng.php.
There are literally hundreds of apartment rental agencies for temporary
places in BA. There's also craigslist. Not to sound obvious, but if you do a google search for 'buenos aires apartments' and the like, you'll come across more sites than you can go thru in a day probably. It pays to take your time and shop around. I had some friends who recently rented a place in Palermo for 800 USD/wk and it was nice, but the place was still being lived when they got there...there were some other problems as well. My point is, the research you put into it will be worth it.
Inflation is in strong effect and the value of the dollar has dropped a bit, but you should be able to find a decent place in Recoleta in or slightly above the range Itchy Mc mentioned above. Depends how much 'luxury' you want.
Check out places in Almagro/Once/Balvanera/Congreso as well. They don't carry the same tourbook cache, but they are close enough to Recoleta that it shouldn't make a huge difference and they will def. be cheaper.
D. Perino deduced: "The Cuban Missile Crisis?...“It had to do with Cuba and missiles, I’m pretty sure.”