Thanks, everybody!
I can drive in Manhattan, I suppose, but I'd like to avoid it if possible, of course. It does seem like trouble...
I suppose I could take Amtrak, but it's like 200 dollars or something, and I have to get to BWI airport--or downtown Baltimore. I'm about an hour from them both.
I had this picture of parking at some lot somewhere in Jersey, and taking a train in. Or maybe even parking at Liberty State Park and taking a ferry to the statue, and then on to Battery Park. By the time I had transfered between a few ferries and the subway up town, it might be time to turn around and go home.

Mrs. Cocker: in my netwanderings, I saw that the Metropolitan's parking garage charges up to $40 a day--up until midnight. I assume that the meter keeps ticking, and after midnight you roll over into a new, and even more costly, day.
Of my options (as I see them: Drive own car, Amtrak, Greyhound, private charter bus; aeroplane) the cheapest, and easiest, is the private bus thing. A local carrier has trips up to New York for about $50, but they're infrequent, sadly.