A GOP-led effort to repeal the biggest parts of ObamaCare would cost about $42 billion less than previously expected, saving more than a half-trillion dollars over a decade, the congressional budget scorekeeper said Monday.

Legislation to gut most of ObamaCare's mandates and taxes, known as Restoring Americans’ Healthcare Freedom Reconciliation Act, would reduce the deficit by $516 billion over 10 years, according to the Congressional Budget Office (CBO).

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The bill is expected to get a vote in the House this week, and it has already been approved by the Senate. President Obama has said he would veto the bill.

The CBO had previously said the bill would reduce deficits by $474 billion, but the estimates have been reduced in light of the recently enacted governing spending bill. That funding bill, which has already been signed by Obama, delays three key healthcare taxes, which each would have brought billions in revenues.

As part of a congressional deal reached on the spending bill, the so-called Cadillac tax on high-cost healthcare plans is delayed for two years and the medical device tax and the health insurance "premium" tax are paused for two years and one year, respectively.

Republicans are looking to pass their latest bill targeting ObamaCare through a budget process known as reconciliation. Under the Senate’s rules, a party that controls both chambers can pass legislation with a simple majority, sending a bill gutting ObamaCare to the president’s desk for the first time.