Hi All,
You've asked a good question. Here's the first response but I would expect more to follow.
Eucatur does offer bus transportation on from Rio to Iguassu Falls. This site is hard to navigate but it will get you there.
http://redeastor.viacaogarcia.com.br/
I personally flew into Iguassu Falls since distances in Brazil are so vast. My best guess is that the distance would be approx 1000-1200 kilometers.