I was in Iguazu in January. Can't be helpful on the flights as I added it to an itinerary to Brazil. While there, I did not rent a car but did hire a driver for a day that took me and three others to the park on both the Brazil and Argentina side (as well as a quick side trip to paraguay). It wasn't very expensive about $15-20 US per person including a ride to the airport the next day. It was great fun, on the brazil side we rode the boats that go right into the falls - literally - got very wet but was amazing.

Have a great time