There are a number of ways to EWR that don't cost and arm and leg, but do take a while.

Kew Gardens to Jamaica - Cab I guess
E train to Penn Station - $2.50
North Jersey Coast Line Train - Newark Airport RR station - like $12.50
Air Train - EWR

At Penn Station you can also walk to the PATH and take that to Newark and get on a Train to the Newark Airport RR station though it is still like $8-10. Plus if you get yourself to Hoboken or Newark, the cab ride from there drops to $30

Just a little help for the newbies coming to NYC. As said earlier though, I beg for EWR trips on the ER and never get them. Lots of 88 trips though and some 73.

Oh and it all depends on the time of day. 5 am show at EWR without a car is a nightmare.