"[T]he federal government is on track to spend at least $11 billion on subsidies for consumers who bought health plans on marketplaces run by the federal government ... [T]his total does not count the additional cost of providing coverage to the 1/3 of the 8 million new people who signed up for coverage who bought coverage in states that ran their own marketplaces ... [If] these state consumers received roughly comparable government assistance for their insurance premiums, the total cost of subsidies could top $16.5 billion this year, resulting in budgetary costs 'far higher' than the $10 million budgetary cost that the [CBO] projected subsidies would cost U.S. taxpayers in 2014."