1. Some roads are paid (Auto Espresso, no cash payment, no credit card payment, only automatic), rather cheap, we travelled 1 week and paid 10 USD. The rental company will give you a car with a automatic electronic sticker. You simply pass the gates and at the end of the rental you pay at your rental company. Easy, not complicated.
Auto Espresso gates.
2. Cheap gasoline 0,65 USD per liter.
3. All the road sings are in Spanish, speed limit in miles per hour.
4. Some roads are in good condition, but mostly the roads are full of holes, beware.
Some cars drive slowly on the left line but it is "normal" to overtake them on the right line.
5. Heavy traffic almost everywhere (mostly around San Juan with many kilometers of traffic congestion), calculate some extra time for you trips.
6. Lots of traffic lights / it will slow down your trip.