(Personal Speculation) The Base Price For The Surface Pro Will Be $899
If we look at the Surface and cover combined as the complete product, the pricing for the Surface RT is heavily comparable to the iPad.
32 GB Surface with Cover = $599
32 GB iPad = $599
This is not a coincidence; Microsoft did this deliberately to give the device the premium feel and to be seen directly against its competition (iPad). So with the Surface Pro, what is there to compare it to?
...makes sense, doesn't it? It even shares the same processor and RAM size.
Applying the same logic as with the RT, the Surface Pro with Cover for 64 GB would probably be the same price as the Macbook Air with 64 GB, $999. So without the cover, it'll be $100 less. Hence, $899.