The Big Dig in Boston cost almost $30 billion in inflation-adjusted money and had nowhere near the impact on the region as a high speed rail system would have in California.
It basically had zero impact outside of the City of Boston.
(And it should have been spent on demolishing that highway, not burying it and not replacing it, then expanding regional rail and transit connectivity in the Boston metropolitan area.)
Or perhaps we should bring up military spending: https://irancost.com/
Silver Line was part of the Big Dig, but I agree the North/South Rail Link should have been part of it. Having no direct connection between North Station and South Station is stupid.
But you can't just get rid of 93
You absolutely can just get rid of 93 within city limits, especially if 30 billion was spent on adding more commuter rail.
The idea that highways must cut through the city, especially one as geographically small as Boston, has been thoroughly debunked.