Just trying some napkin math...
Some very surface-level searching shows someone claiming a total societal cost of ~$7k per deer collision.
Supposing it's a $15m construction and could last 30 years without major maintenance, then it needs to stop ~71 events per year to "pay for itself".
To be fair, that is the cost of collisions rather than any near-misses and traffic problems, or the less-quantified ecological cost.
The article linked by JKCalhoun lists
Deer $6,617
Elk $17,483
Moose $30,760
That seems well within reason, an article said about 1 deer collision prevented per day in the spring and fall high season. Having driven through the area and seen dashcam footage of collisions and near collisions, that $7k makes sense to me. I've known several people that have hit deer on the highways here, and I'm actually surprised if anything that the number is that low.
So my gut feeling is that it actually has slightly better returns than expected from those numbers.