Some areas of the country is better to be explored with a car. Patagonia is one of them. In fact, some said that it's better to rent a car in the city of Bariloche than in any other Argentine cities.
There are three ways to rent a car in Argentina.
The first way is to find it on the Internet, either through some search engines or the websites of rental companies. This is the most expensive way. The cheapest option is around US$70 per day.
The second way is to visit the office directly. You will get a cheaper price at US$55. If you pay by cash, there is any extra 10% discount.
The third way, also the best way, is to ask your hotel or hostel to help you. They have connections to rental companies. In my case, I got a very good deal at 13,000 pesos (US$35), paid by cash. It's a very new Fiat sedan, with only 4000KM in odometer. There is a large screen that can work together with your Android phone for GPS purpse. The similar model would cost US$90 if you book it online!
Enjoy your drive in Patagonia!