IMO the route with the lowest tolls would be to get on I78 near Liberty Harbor to I287 to the NY Thruway north (I87) to I84 all the way to the Mass. Turnpike (I90). There are tolls on I87, on I84 at the Newburgh/Beacon bridge and on I90.
A second route (the one we use) is to take I78 to the Garden State Parkway north to I287 east over the Tappan Zee bridge to I684 north to I84 to I90. There are tolls on the Parkway and the Tappan Zee bridge that I believe are a higher toll cost than the first route. The second route is longer though, so higher fuel cost and more travel time.
FYI, RVs are allowed on the Garden State Parkway in NJ but not on any road with "Parkway" in the name in NY and CT due to low bridges.
