No way either of these consoles will be $350 w/o some heavy subscription plan. That's either $50 more or $50 less than comparable PS3s/360s.
My stupid guess is that $400 is the absolute lowest, but both the PS3 and 360 will get significant price drops.
Another thing, the current PS3 controller is going for $55, so how much with the PS4 controller end up costing? PS4 controller is the PS3 controller + bigger battery + touchpad + lightbar + better motion sensing junk + headphone bit - analog buttons.