Cost estimates for a key portion of President Barack Obama's healthcare overhaul law have ballooned by $111 billion from last year's budget, and a senior Republican lawmaker on Friday demanded an explanation. House Ways and Means Committee Chairman Dave Camp, R-Mich., wants to know by Monday why the estimated cost of helping millions of middle-class Americans buy health insurance has jumped by about 30 percent for an eight-year period, from 2014-2021.