According to a rumour posted by Forget the Box, Nintendo wants to make a profit on the Wii U from day one and as such the price is likely to be $300 (typically this means something like £270 over here, in a best case scenario) at launch. The site states that the production costs for the Wii U, including everything from CPU, GPU and touchscreen would come in around $180.
Right now it's just an educated guess based around the notion that Nintendo wants to make a profit on the hardware from day one, but who knows if the slow early sales of Nintendo 3DS (pre-price drop) may have altered Nintendo's position in this respect.