isint the bus from NYC to EWR cheaper? I know it wouldn't work if you have luggage etc, cuz you'd need to schlepp on the subway to get there, but if you don't have too much luggage and have time...
The cheapest way that I know of to get from Brooklyn to EWR is:
1) Take the subway to the World Trade Center
2) Take the PATH train (using your metro card) from WTC to Newark Penn Station
3) From Newark Penn Station, walk across the street to the Hilton Newark Penn Station which has a complementary shuttle to the airport every 30 minutes IIRC.
Not for everyone, but if you must know the cheapest way...