Hostels are sprouting up in Rosario like whiskers on Che's chin. A comprehensive guide to most of them can be found at the tourist office. They are generally located in the downtown area and along the waterfront.  If you look around a little it is easy to find a good bargain and a good group of likeminded travelers. Reservations are a good idea if you are arriving on the weekend. Mid-range hotels are also abundant and are a good option if you are sick of the "backpacker" circuit. Again the tourist office has a list of hundreds of places to stay, with options from five stars on down.