Nuestra Parrilla (or Freddy's Parrilla - both the same place despite both names being used online) is a San Telmo institution. The food is cheap, hearty and tasty and the best known item is the choripan, a chorizo (ie. housemade sausage rather than the heavily smoked type I'm used to in Spain) in bread. It is a hot dog, but a damn fine version where the sausage is the specialty and cooked over the coals of a parrilla.
Nuestra doesn't have a sign or at least not one that I saw. But the people eating inside and outside and the smell wafting around the south entrance to the San Telmo mercado made it easy to spot (and Google Maps helped too).
For ARS35, the sausage choices are chorizo and morcilla. Both are delicious, probably the chorizo moreso with a deeper meaty flavour. The morcilla has the distinctive flavour albeit not that strong but still good. The textures of both sausages are nice and smooth. I went back a few days later (the carpark choripan in the Sunday feria smelt great but I couldn't justify it for ARS65-70) and tried the vaciopan (beef flank in bread) for ARS80. It was a long roll with two big slices of meat cooked through. It was chewy as expected (I think rare isn't an option in that kind of place particularly when the meat is cooked until it is ordered) but it tasted nice my incisors had a good time tearing away at it.
All the choices, in particular the flank, were improved by a healthy serving of both chimichurri and salsa criolla which added herb flavour, texture and lemon tang.
It isn't the best of the meat places but it may be one of the cheapest and possibly the best value for money. Satisfying.