Paul Thurrott is definitely credible. You can read a little about him at this Wiki entry
, if you're so inclined. The short story is that he's a well-established technology reporter.
Okay, then I'm taking his second claim a bit more seriously now.
The new Xbox will cost about 500$ for a normal unit, or 300$ for a subscription model (no details on this) when launched in November. Also, a $99 Xbox 360 codenamed "Stingray" will also be released in November because the Durango will not be backwards compatible with 360 games.