There's a very famous cafe at Cordoba and Carlos Peligrini called Cafe Exedra. At night, particularly after about 11:00 PM or so, if you see a woman there it is more probable that she is a prostitute than not. You can see men going there, in full public view, to sit and talk with the girls and many times they leave to go to telos nearby (which are very common throughout the city).
On many (most?) blocks throughout the city (at least downtown and surrounding neighborhoods) there are "privado" apartments where men go to see prostitutes, brought into an anteroom and lined up for their choice.
There are a number of clubs throughout the city, and heavily concentrated in Recoleta and Microcenter (although a number of them have closed recently) where men can go to sit and talk with prostitutes in a club environment, make deals and then leave to go to a telo.
BTW - remember that prostitution is a constitutionally-protected right in Argentina - although pimps are not allowed. The privados are not really legal because of this. The clubs make money from the drinks the girls talk the guys into buying (really, really expensive, but it's known what's going on, obviously). Something like Cafe Exedra, and a bar called New Port in Recoleta (at night) are exactly what the constitution was talking about.
I know two Argentinos (acquaintances) who are currently having affairs with younger women. While both are supporting the girls in some fashion, one actually pays for her apartment and university and bought her a car.
My brothers-in-law (ranging from 20 to 27), most of whom work in verdulerias (around Constitucion and Parque Patricios) are accosted all the time by older women (and some of them are really old - in their 80s). They have been offered everything from cellphones to computers to having university paid for, to have sex with them.
Sex is thought of very differently here. I've heard an Argentine woman say "I don't care if he's out screwing someone else as long as I don't know about it and it doesn't get back to my friends". (and have heard that it is a not uncommon attitude but can't confirm that)
Yeah, I think Argentinos are more promiscuous than where I come from. And I'm not saying even that that's a bad thing (except I can't help feeling anxious when it comes to my sisters-in-laws who are like daughters to me!!!).