If it was being built today, it would probably take twenty years and have to be retrofitted after another ten.
It's very fortunate that we Californians had ancestors who actually knew how to do things.
That's because the Golden Gate Bridge project was conceived of as a bridge project.
The current project is a political-rewards-masquerading-as-public-works project. The goal was never to complete the bridge, but to spread cash around to the politically connected firms, unions, and public employees working on the project.
If you've ever wondered why such projects always go over budget and never seem to end, it's because that is what they are designed to do-- every political interest group to which the pols are tied benefits from hiking the cost and dragging it out.