Uhh, we just approved $54 Billion for Sound Transit 3, which adds 62 miles of rail spanning from Everett to Tacoma, so no, light rail isn't dirt cheap. It is very effective at moving people cheaply though, and is a big economic boon to this city.
Going from Capital Hill to UW in under 5 minutes on the train, versus a 10 to 20 minute drive is amazing!