They sell loose tea in any Tea Connection: https://www.teaconnection.com.ar/pages/tiendas
Tea selection (English Breakfast included): https://www.teaconnection.com.ar/collections/te-everyday
For cheap lower-quality national tea, Coto carries it as mentioned above...
https://www.facebook.com/events/511371846379417/ - free weekly event. There's a spanish table as well as english, french, portuguese and italian. I practice french, but there are always a few foreigners who come to practice spanish.
Just by seeing how they compare price of units in the UK to kilos in Argentina, without even trying to make a simple conversion, tells me a lot about objectivity of this article. Numbeo data is a lot more objective and up to date...
Private lessons is the fastest and most effective way. 2 classes/2 hours per week is plenty. 20 hours/week in a tourist school is a waste of time. Better spend this time practicing spanish with the locals and absorbing learned material. You'll save both time and money.
Aerolineas' Cabildo and Congreso de T. office. Paid in cash. The 20% charge is applied to the price. Plus they charge you a small fee for paying in cash.
One tip: make an online reservation just before you head to the office. This way you won't have any surprise differences in price. Bargain...
In case anybody bought tickets from www.flypluna.com, you'll probably need to consider alternatives. I think they are officially out of business as of thursday night.
Private classes are the way to go if you're serious about learning the language. James, if you're interested, PM me for the info of the tutor I used. He's a native speaker of course.