That youtube clip is from 2004. I was just in SF this spring and walked across the GGB. The railing is no longer open like that, they have sort of high mesh fencing, about the same as stucco wire mesh, that goes all along, quite high in some parts. And they have phone numbers posted all over for those who need counselling regarding suicide or perhaps another mental problem.
As to some actual specs of the bridge and the cables used it its construction, this picture tells a lot. How this would relate if at all to the cost of a net under the bridge, I am not sure.
