Per their vote count, the GOP can't afford to lose more than 17 Republicans (it would be 16, but two Democrats won't make the vote), but with up to to 22 members of the GOP conference saying they will or could vote no, the vote could come down to the wire. In one sense, it doesn't really matter what happens, because the budget isn't going to go anywhere even if it does pass. But House Republicans have made a big deal about passing budget for the last few years and they apparently don't want to fumble the ball in 2014.
But even more bizarre than their obsession with the budget process is the fact that of the 22 members who might vote against the bill, all but four would oppose it from the right, even though it is a Draconian plan that would end Medicare as we know it, effectively gut Obamacare (including insurance subsidies), and slash spending on countless domestic priorities, all while giving a huge tax cut to the wealthy. By any reasonable measure, it is a conservative dream, but for some on the right, it isn't enough.
If I were to bet, I'd bet pretty heavily on the bill passing, but the fact that there's any chance at all that a bill calling for the repeal of Medicare might fail because it isn't conservative enough is a pretty clear illustration of just how far out of the mainstream the GOP has gone.