All light rail cars are custom in the same way that every airplane is custom but we wouldn’t say that a 737 is expensive because of the seat and entertainment choices.
Sound Transit operates LINK (what gp was talking about) and Sounder (not light rail, operates on BNSF tracks, coaches are made by Bombardier and seem to be in use by many commuter rail systems). Not sure what you're referring to.
That's LINK light rail, operated by Sound Transit. Here's an article about the (new) cars they use: https://www.soundtransit.org/blog/platform/new-link-light-ra... -- I get the impression all light rail cars in general are made to order per specifications, rather than off-the-shelf.
Before it was built is when they said they would be custom cars.