I would refer you to my thread and post on cuevas:

http://www.flyertalk.com/forum/argen...ge-cuevas.html

I suggest you change money at a cueva. It's not risk free but its much less risky than dealing with some guy who's there today, gone tomorrow on Florida.

You will get the best rate. Then you can pay for everything in Pesos and not be trying to peddle foreign currency in restaurants, etc.