Bay Area commuters paid $50 million for that monster crane that was used to help build the $6.4 billion eastern span of the Bay Bridge — only to see it later handed over to the builders for free.

Now, it turns out, those same builders are cashing in on it — putting it to work constructing a new taxpayer-funded bridge in New York.

“The optics are hard, but it was the right thing to do,” said Bay Area Toll Authority spokesman Randy Rentschler.

The huge, custom-built Left Coast Lifter, which for years was a fixture on the Oakland side of the span, weighed anchor at the Port of Oakland in December for a 6,000-mile voyage down the West Coast, through the Panama Canal, across the Gulf of Mexico, up the East Coast and into New York Harbor.

The Lifter has been rechristened the I Lift NY super crane and has been put to work on the New Tappan Zee Bridge going up over the Hudson River. For the next three years, it will be used to hoist heavy pieces of the new bridge in place, and then to help dismantle the old Tappan Zee.

New York Gov. Andrew Cuomo praised the crane for saving the state money by reducing labor costs and cutting project time.

“Any crane that saves the state of New York over a billion dollars, I love,” he said. Cuomo really should be loving Bay Area toll users who footed the bill for the crane.

Back in 2006, when American Bridge/Fluor submitted its winning $1.4 billion bid to build the Bay Bridge’s self-anchored tower — the world’s largest — it proposed having the floating crane specially built to help lift the 1,300-ton steel sections into place.

The company wrote in a provision allowing it to keep the crane afterward. “It was factored into their winning bid for the construction of the project,’’ said Metropolitan Transportation Commission spokesman John Goodwin, who added that it’s no different than the contractors being paid $250 million to demolish the old bridge span and also profiting from the sale of the scrap of the old bridge.

Besides, by giving the crane away, the state wouldn’t be on the hook to sell a one-of-a-kind piece of equipment that it had no other use for, say bridge officials.

American Bridge/Fluor, however, found a buyer. They “sold” the crane to Tappan Zee Constructors — the consortium they are part of that’s building the new New York bridge.
As for how much they were paid?

“We are not releasing that type of information,” Tappan Zee Constructors spokeswoman Carla Julian said. She did tell us, however, that the crane will be returned to American Bridge/Fluor once the consortium is finished building the bridge.

State Sen. Mark DeSaulnier, D-Concord, who convened a series of Transportation Committee hearings this year over the runaway bridge costs and construction defects, asked whether Californians got cheated in the deal.

“I have to look at the contract,” he said recently when we informed him of the crane giveaway. “But if toll payers of the Bay Area paid for this — and (officials) saw some use for it — they should get some of the value out of it.”