There are too much hypothetical numbers on both opinions. The reality is actually more straight forward.
The assembly, design, architectural, engineering of the bridge are done by American in America or developed world based on bid and performance. So that part of the money will be where it is regardless of we outsource the components of the bridge to China or not.
The components of the bridge, will cost certain amount in steel and concrete and the labor / profit on top of that. The material cost is fixed regardless of who build it, but the labor and profit is the one that is debatable.
Basically, we have two numbers depend on who won the bid and where to build it:
1) All American: assuming American labor is 2x as productive, we have labor + profit staying in the US that goes around with multiplier for the economy. However we have loan to pay back for the additional cost of the higher price. That's 400M more from California to put back into the US (most likely the steel belt states and the wall street).
2) Chinese with American QA/supervisor: the material cost is the same and the labor is cheaper and assuming the Chinese government is subsidizing with low profit to get future marketing material, technology know how, or just plain economy of scale because they will build identical bridge parts in the future. The labor and profit will be gone from the US (lost potential profit in the steel belt and the wall street). But the debt load of California and local cities would be 400M lower.
Assume steel and concrete is a commodities that get shuffle around the world and every producers are selling as much as they can produce (because China is buying up all the steel and concrete in the world, they are our primary concrete export customer, and our auto industry feel the cost impact from the steel tariff the last president setup). We would be looking at the (labor cost + profit) x multiplier vs 400M saving x multiplier.
Assume the same or similar multiplier number, as a whole if the labor is more than 400M (likely since the bid is 1.6B), the economy would benefit more if it is made in the US.
In a "small government" world where California is paying for most and the steel belt states are getting the most, California would make the selfish decision to buy Chinese instead, regardless of which make more sense in the bigger scheme.
Small government doesn't always give you efficiency as long as there's participant that isn't playing by your rule or benefit you in return.