Thank you for that helpful response; offering to pay a few months in advance hadn't occurred to me.Regarding the 50% increase: I think that increase is more less in line with inflation (might even be slightly below it). Assuming that you have a peso contract, I don't see this as a total rip off per se. If the apartment is in bad shape, that's another story then.
Generally speaking, I think there are a lot of empty apartments throughout the city as the annual return (from the owner's perspective) is probably in the 1-2% region. Given the potential problems with non-paying renters, a lot of the apartments are kept empty to avoid potential problems. I think also the ley de alquileres introduced last year didn't really help to increase the offer.
From a renter's point of view: if you can demonstrate that you have enough funds to pay the rent (even prepaying 6 to 12 months), I think you should have no problem to get a good deal now though
About the apartments deliberately held off the market, and the effect that has on housing prices -
A majority of voters in Berlin wants city hall to expropriate major landlords such as Vonovia and Deutsche Wohnen to help reduce rents in the German capital, provisional referendum results showed on Monday.
The vote passed easily Sunday, with a nearly complete count reflecting 56.4 percent of voters in favor of the measure.
If it can happen in Germany, it can sure happen here, especially with Peronists in power.
And, yes, I did just offer a link to the Daily Beast, because when I linked to a story in RT, I was told that didn't count because "it's the Russian government!", a comment I will definitely return next time somebody links to a story in the BBC...