One comment about 1000 pesos passing through fingers with BA night life - I regularly send my 19-year-old out for a complete night of partying with less than 200 pesos - and she usually doesn't spend all of that. She and her friends seem to party quite well. But they don't go to expensive high-end places either. Partying can be done quite cheaply here and everyone I know who does is quite happy with it. I don't know anyone who is young, does drugs even, drinks a lot when they are out, and comes close to spending more than a couple hundred pesos at most in an outing (and through having three teenage girls here, I know quite a few young partiers).
You're also making an assumption that he has to take $1000 USD out of his money to buy a return plane ticket. That's an extra 100 pesos a day over his entire trip! What about his ticket to get here? I suspect that his travel money might be a different budget that he already has taken care of. EDIT: I should have read the OPs following post, first, before responding to this
Also, with the money he has saved, he could most likely make at least one less trip to Uruguay to get that money at the tail-end of his trip.