If you do not want to complicate your life much, I recommend the use of taxis or remisis (which is another way they have in Argentina to call them).
Here is a short list of one of Rosario’s taxi and remission companies and their phone numbers:
Your Radio Taxi – 4311111/4544000
Radio taxi – 4380000/4382222
Rosario taxi – 4566666/4566639
Remises Cruz del Sur – 4851515/4853535
Remises City of Rosario – 4724921/4724920
The rates are around 3.50 (€ 0.70) pesos lowering the flag (a little more in the case of remises) and then goes for every 100 meters 0.18 pesos (€ 0.03). Calculate that apples is Argentina usually have 100 meters. It is advisable to ask for the ticket, so you can check what they have charged you or at least the driver thinks you are going to check it.