A bad one if you think that that are hotels of around 30 dollars at avendida de Mayo"Quimera" said:Many cheap hotels on avenida de Mayo, around 30 dollars a single room (no less).
some of them could be:
Hotel Marbella http://www.hotelmarbella.com.ar/
Hotel Mari Plaza (people from my job delegations go there), on Bartolome Mitre Ave. http://www.mariplazahotel.com.ar/
cheaper places could give you a bad surprise...beware.
I'm not an expat, I'm porteña, I've been trip advisor for years. So, at your service.