You can read in the shitty south america on a shoestring lonely planet (2004) that at Sheraton Iguazu is a lunch buffet for only US$10. This is not true, I don't know, where they got this information from. The Sheraton lunch buffet was in april 2005 60 Pesos, these are 15 EUR, means nearly US$18.
We also didn't see any other 'backpacker' inside the lunch room, as they wrote in lonely planet....