We were in Argentina for a week this past November, on our own. Based on previous advise, we went to a Cambio and exchanged a 50 dollar US bill into pesos, only to find the locals really wanted their tips in dollars. Also, as mentioned previously, when using a US credit card, the amount charged will be lower.  However, we learned that it took several days for this to happen.  If we checked immediately after a purchase, it still showed an amount reflecting the 'official' exchange rate. So...just