The total cost to implement Obamacare in Massachusetts surpassed a half-billion dollars yesterday, as the Health Connector board agreed to seek an additional $121 million in federal funds to try to rescue the money-hemorrhaging health exchange.

“This is now Massachusetts’ Big Dig I.T. project,” said Joshua Archambault, a health care expert at the Pioneer Institute. “The decision was completely irresponsible to taxpayers, with very little uncertainty we’re going to get the end result that we want.”

The board approved a two-track plan yesterday — invoking an emergency provision to sidestep state procurement laws — to award a no-bid contract to Minnesota-based Optum. The company will, in turn, subcontract with hCentive — which it holds a 24 percent stake in, as the Herald first reported yesterday.

Connector officials insisted the exchange is so broken they had no choice.

“The reality is, this is it,” said Sarah Iselin, the state’s Obamacare czar. “When we look at what we can reasonably do for the fall, this is it. I wish we had more choices, but we don’t. We’re making the best of a really lousy situation.”