I am not in Mar del Plata but I spent there my last three Argentinian summers. There are some expats there, indeed, but I don't know personally any (I knew one, but he left).
I haven't heard much about United States dudes here. One bartender at Bruno told me that, after summer, they're all gone, and another at Alem said that the last time a United States guy had come in was when the sub crashed... the guy was there from the States for the S&R, apparently.
In Mar Del Plata there are many beer stores, but they are not cheap. Cheap beer is sold in supermarkets and it is really piss... where are you from? Almost anywhere in the western world there is a beer culture that here is just starting out.
However, if you go to a cerveceria early in the evening they usually have promo 2x1 on pints (such as between 7PM and 8PM). Take into account that here before 9PM nobody goes out for dinner, so it is really an after-work beer.
Oh, man, a litre of IPA for a little less than two bucks is super cheap compared to where I've been out in CO. I've been really pleased with most of the beer prices.
Three packs of marlboros for 200 pesos is also pretty good considering I've been paying a little under $7 USD per pack.