Old article from before they implemented them (the article mentions the budget proposal being $4 million, it's turned into $64 million and counting).
$4 million for one canopy.
FTA:
The canopy, still in prototype form, would be designed and built over the next two years at a cost of almost four million dollars, with the first installation scheduled for 2015 at the 19th Street station in Oakland.
The project is expected to cost $4 million per entrance.
https://www.ktvu.com/news/bart-seeks-public-opinion-about-planned-improvements-for-sf-stations
They are government buildings.