Here is a suggestion that uses existing infrastructure to provide easier access to the Metro North Hudson Line for residents of Orange and Rockland Counties.
The tracks of the Metro North Hudson Division pass directly beneath the Bear Mountain Bridge. Currently, commuters who cross the Bear Mountain Bridge can either drive north to Garrison and take the train from there or drive south on winding overcrowded route 6/202 to Peekskill. Some continue on to Cortlandt or Croton Harmon stations.
I propose that elevators and a people-mover could be added to the Bear Mountain Bridge with little impact on the bridge. A railroad station could be added at the base of the bridge. The people-mover could extend to the parking lots adjacent to the Bear Mountain Inn - which generally sit empty on weekdays.
Additionally, if West Shore Line commuter service were implemented, a second station and elevator on the west side of the bridge could be used to transfer West Shore passengers to the Hudson Division.
In terms of the added convenience for commuters this should be a very cost-effective solution, since it makes use of existing infrastructure. Certainly, when compared to adding new roads or rail lines, the cost should be quite low.