Ballpark Estimate: $37 Million Dollars + Interest
The Golden Gate Bridge in San Francisco was built over a four and a half year period between 1933 and 1937. It is the second largest suspension bridge in the United States.
The bridge cost $37 million, but was funded by municipal bonds that cost an additional $39 million dollars in interest. The entire cost of the bridge was paid for by tolls before the final bonds were retired in 1971. A rough estimate of the $76 million the bridge cost (including interest) in 1933 is over $1.2 billion in 2007 dollars.