AdWeek notes that NBC has sold nearly all of its ad units for XLVI in February, 2012 and at prices reported to be as high as $3.5 million per spot. That compares to the reported $3 million per spot asked by Fox for XLV.
Of course, you should take any public ad pricing reports with a bag of salt because, as AdWeek notes, those ads are almost always sold as parts of packages, so the "sticker" price is typically only an indicator.
The article also notes that NBC has sold out nearly its entire ad inventory for this season.
America is indeed, ready for some football.