The following is from Wikipedia:
"The PlayStation 3's initial production cost is estimated to have been US$805.85 for the 20 GB model and US$840.35 for the 60 GB model. However, they were priced at US$499 and US$599 respectively, meaning that every unit was sold at an estimated loss of $250, contributing to Sony's games division posting an operating loss of ¥232.3 billion (US$1.97 billion) in the fiscal year ending March 2007."
Theyve probably reduced the production cost since then, but at the same time they've also lowered the price.
The Xbox360 also sold at a loss from it's inception, and the red ring of death recalls also cost them. But I am confident MS still doesnt lose as much on each unit as Sony does.
As for the Wii its production cost is a closely guarded secret though some have speculated on what it is. Its architecture is similar to a gamecube, so they went with the cheap route. It shown in their games and limited abilities. So it is safe to same that they are making a handsome profit on each console sold. A claim Nintendo itself has backed up with official statements.







