I expect $400 at least for the WinRT version. $500 seems more likely. Which would still make it compete with the iPad, but not as easy a choice for consumers. $450 seems like the sweet spot, but it still sounds optimistic.
The pro one... I wouldn't be surprised at $1000. It'd be a mistake, but it wouldn't surprise me. I wonder if they can sell these things at a loss by subsidizing them from app sales, sort of like with the 360.
Edit: so, yeah. What Minh said. *cough*