A bus leaves twice hourly from the terminal to the entrance on the Argentine side of the falls 20 Pesos return. Most hotels have the timetable. Tell the bus driver if you want to stop along the way. On Sept 25, the bus was 25 each way, so 50 pesos r/t.
Frequent buses cross the border to Foz do Iguaçu where you can change to a bus to the Brazilian side of the falls
Some buses cross to Ciudad del Este without stopping in Brazil hence, no need for Brazilian im- and emmigration
There is a ferry crossing directly to Paraguay look for the sign on the corner Av. Missiones and Brasil. About twice hourly during daylight. 10 Pesos for foot passenger. On the Paraguayan side walk up to the main street and take any bus going to the right don't believe "Taxi" drivers telling you there is no bus, they are just up to overcharging you. You can pay the ride in pesos 2 Pesos. When you arrive at the roundabout about half an hour later you are in the centre of Ciudad del Este, for the bus terminal you have to get off earlier.
Taxis
operate with fixed prices which makes the distance to both parks from your hotel irrelevant. A trip from your hotel in or near Puerto Iguazú to the Argentine park or vice versa costs 60 AR$. Round trips are advertised as double but most taxi drivers will do the trip for 100 AR$ if asked. Do not be amazed if the very same driver waits for you for hours. Taxi drivers will store your luggage in their taxi while waiting. A round trip from your hotel to a supermarket in Puerto Iguazú costs 10 AR$.