Is the Prospect Park rink open yet?Oh cheapest ice skating is at Bryant park. It is 17 for skates. Be prepared that it is insanely packed on the ice skating rink.
You could hit TKTS at the Seaport, walk over to OWO (they serve alcohol at the top) and then do ice skating at the World Financial Center (now called Brookfield Place). Wear a Wake shirt in case I'm out and about.