In 2012 Medicare, Medicaid, and Children's health funding was $732 billion. And I don't know how you get rid of SS since the government would still need to make payments that are higher than any typical basic income level.
You could transitionally subsume SS by making SS benefits, as a special transitional case, non-cumulative with BI -- how this works:
(1) eliminate separate SS tax when you establish BI (probably keep a tax of about the same level overall rolled into general income tax, you probably need it to fund BI, but you no longer have dedicated SS contributions)
(2) The SS eligibility you have earned from your past contributions remains, except any time when you would get SS, your BI is deducted from your SS benefits (so you never get less benefits from BI+SS than you would have gotten from the worst of the two, but also never more than you would get from the best of the two.)
So, over time SS withers, and to the extent its duplicative its effectively eliminated immediately, but no one loses the minimum guarantee they had already secured from SS.
http://www.cbpp.org/cms/?fa=view&id=1258