Mik,
There are always options, but do they justify the savings? Liberty Harbor is just an fenced off area of a parking lot, no trees, asphalt surface and tight spots. But its draw is LOCATION, LOCAYION, LOCATION. All other options are at least an hour away.
You kill two hours of your day just riding into town, and parking isn't cheap or easy to find. Plus, after schlepping around NYC all day, you are pretty beat. During the work week, there is a water taxi that you ride to a pier that is at the foot od Wall Street. I like the fact that the water taxi picks up drops off right at the marina dock, which is about 100 yards from your parking spot.
A couple more options you can consider are
Croton Point Park and
Black Bear Campground.
