Liberty Harbor is fine if you want to tour the city . You can take Ferry into wall street area directly from park. Or there is a train about 8 blocks away.
I stayed there before no problems. As far as price, this is NYC we are talking about. $80.00 is actually a bargain for NYC.
Yes it is basically a parking lot with W/E and a dump station. It is safe and has a decent bathroom. If you are looking to tour the city and use your RV as a hotel Liberty is perfect. Liberty is a 20 minute ferry ride to city. You can see statue of liberty from the CG.
I have also stayed at Croton Point Park.
More of a traditional camping atmosphere. It is a Westchester county park about a hour train ride to grand central station. Train station is located right outside the park. Croton Point is located right on the Hudson River. I have done both places and would return to both.
Croton point parkLiberty Harbour