Probably the cost issue with the Gamepad is that it's arguably over-designed. It's got a camera, and IR sensor, touchscreen, gyros (from what I've read on par with Wiimote+), mic, NFC, rumble, and lord knows what other gimgams buried in it. The NFC might turn out to be a smart move if the Amiibos take off, but that seems pretty damned unlikely. If it was just a controller with a touchscreen, then it could reasonably sell for $60 and be a genuine accessory for multipad games. But that doesn't appear to be in the cards.
Although I wonder if the tech for streaming two pads at the same time just isn't feasible despite internal hopes that they could figure it out. For all the WiiU tech bashing, the gamepad streaming is extremely impressive.