this website is has good prices for a lot of stuff:
http://www.destinoiguassu.com.br - including car rentals.
If you don't pick up the car at the airport, you save money. But it also sells packages (passport style) to attractions around Foz. They actually had something that fit my needs!!!!
http://wikitravel.org/en/Foz_do_Igua%C3%A7u has some interesting information in English about Foz.
And to visit and buy tickets for Itaipu, the best bet is to go to their website:
They also give other kinds of information.