For that price tag be ambitious and go for a crossrail level project. Bring in NY and the feds to also spend that much and then do a rail tunnel from Hoboken to somewhere in lower Manhattan to Atlantic terminal.

Build a Union City station for the new Gateway tunnels to midtown or on the old tunnels when they're closed for renovation.

PATH to Secaucus Junction or up along the existing ROW alongside the Heights and Union City.

Fully grade separate the light rail and then automate it.

Extend the West Side Avenue Line of the Light rail to Newark Penn. (More expensive if it's done alongside the idea above to fully grade separate it.)