Well, depending on the exact specs of the thing I think my price range will be like $450-$550. It never costs more than $599.99, never. Unless MS doesn't want to sell any. Even then 600 is too much.
Also my guess is 12gb of ram something custom built GPU about equivalent to a GTX 1070 obv ~6TFLOPS of power, day one occuls rift support, native 4K first party games day one too.