It's not wildly unlike a normal highway bridge. That's about what they cost.

Also

Aside from the freeway overpass, the construction continues. Workers are building a second large structure that will bridge a local road and connect the overpass with the surrounding steep hillsides. Once that’s completed over the summer, they will haul in 3m cubic feet of soil – enough to fill half of the SoFi stadium – to bridge the gap between the overpass and the surrounding landscapes. The construction teams will also build berms to block out noise and light, and add wildlife-proof fencing along the freeway.

I actually think the ecosystem benefit here will quickly payback even that large of an investment, an open air, safe feeling wildlife transit corridor for wildlife can easily be a keystone piece of architecture in maintaining a regional ecosystem and flow of nutrients/migration of animals. That isn't even bringing into the picture the MASSIVE cost savings that a reduction in wildlife-vehicle collisions inherently provides.

Benefits of crossings

The U.S. records more than 1 million wildlife–vehicle collisions each year, and that is probably an undercount because of unreported incidents.3 These crashes cost more than $10 billion annually in repairs, medical care, and lost productivity, and they cause about 200 deaths and 26,000 injuries annually.4 According to the Federal Highway Administration, wildlife crossings can deliver key benefits for drivers and wildlife, including:

Crash prevention: Wildlife crossings with fencing can cut large-mammal collisions by more than 80%—and up to 97% for certain species, including deer and elk—making them among the most effective ways to improve driver safety and wildlife connectivity.5

Cost savings: Each prevented wildlife–vehicle collision can save thousands of dollars—more than $19,000 per deer crash, $73,000 per elk, and $110,000 per moose—in vehicle, injury, and wildlife costs, making well-placed crossings a strong investment.6

Habitat connectivity: Roads, fences, and development break up landscapes and block wildlife migration, limiting animals’ access to food, water, and mates, which can cause population declines and reduce biodiversity by up to 75%.7

Communities throughout the country are investing in a range of wildlife crossings to improve public safety and protect vulnerable species. (See Figure 2.)

https://www.pew.org/en/research-and-analysis/fact-sheets/2026/01/wildlife-crossings-save-lives-cut-costs-and-protect-animals

Relevant article

https://y2y.net/blog/how-wildlife-crossings-revolutionized-conservation/

Another relevant study that looks interesting

https://pmc.ncbi.nlm.nih.gov/articles/PMC9753749/

That's fair, and knowing nothing about it at all. Everything has gotten more expensive. The article states that some price index for construction has gone up 67% since 2021. But i have no idea what the cost is of a normal bridge, much less one that has to deal with the added burden of being a wildlife bridge. I assume that made it more expensive because they needed to make sure none of that wildlife/eco system would unnecessarily wear the bridge.

I dunno just my 2 cents

Building a large bridge like that, with the added complication of holding lots of protentially water soaked heavy soil and trees roots that try to break through the bottom isn't cheap. More or less the same reason why roof-top parks are prohibitively expensive in most cases.

What I find a bit surprising is that they didn't go for a tunnel for the cars, which is typically cheaper to do.

The one across the freeway is big. Real big. Then there's another bridge across the tributary road that's not as big. Still pretty big.

Roof them with solar panels. Should be cheaper than wars for oil.