The Heritage Foundation has now come out against immigration reform, without exactly taking that position, indeed while claiming to take the opposite position, but calculating that adding that many citizens is going to cost $6.3 trillion in new Social Security and Medicare spending, education spending, welfare payments, and what not. McGrubio, as Laura Ingraham has dubbed the troika of Republican senators leading the pro-reform push, have been arguing preemptively that that number is brazenly exaggerated.
Of course these costs would increase, but so would revenues. In 2007, the Congressional Budget Office estimated that the immigration reform bill then under consideration would increase spending by around $23 billion but revenues by just more than twice that. The CBO apparently hasn't scored this bill, but Brian Beutler of Talking Points Memo has a good run-down here of what's changed since 2007, and of course his point is at odds with Heritage's.
This is an old conservative play--go after the cost of something, which permits them not to be against the idea per se, only against its fiscal ramifications. "We're not against immigration reform. Quite the contrary! We're just against the cost of this particular bill." It's a cousin of the old saw one always heard back in the Cold War days: "We're not against arms-control treaties in general at all, but we are certainly against this one," which just happened to be the case with regard to every single one.
Meanwhile, Politico reports that the Senate Gang of Eight members think they can get a dozen or so GOP senators. This is still too early to get a good whiff of where the wind is blowing. If the pro-reform people get Rand Paul, then we probably will see a bill pass. Is that the smart play for Paul? I don't know. I'd guess probably not. If he is sizing Rubio (pro-reform) and Ted Cruz (anti) as possible 2016 opponents, I would think that Rubio is the more serious opponent of the two, and therefore Paul would want to position himself opposite Rubio and then just hope/assume he can outduel Cruz on fundraising and other issue.
Which is another way of saying that it isn't yet clear that the GOP's DNA will permit reform. And if it dies, that really could lead to a major schism, aside from saying hello to President Clinton 45 and at least three new liberal Supreme Court justices!