The contractor operating the crane that collapsed into the No. 7 train excavation work pit last week was by far the low bidder on the job, say sources.

Yonkers Contracting bid $116.2 million for the contract at 11th Avenue and West 34th Street — $21.3 million less than the second-place bid from EE Cruz & Co., a New Jersey-based heavy-construction contractor.

Investigators believe a cable holding up the boom of the Manitowoc 4100 crane failed in the accident, which killed hard hat Michael Simermeyer, 31.