Rail, ties and clips/pads are cheap, relatively. Any of us could lay rail, with more or less mechanical assistance. The ballast is not too expensive, but the grading and subgrade renewal starts to add up. All the office work of adding the Andover Branch (since NJT would have to be insane to call it anything smacking of further distance) into the schedule, both public and internal, won't be too cheap either. But, I suspect that cutting the Andover Branch into the existing signal system will be the really expensive part.
Paying off the mob, the Christie, Menendez, Cory Booker, Steve Garrett (NJ 5th) and Rodney Frelinghuysen (NJ 11th) campaign funds, and the second mortgages on the beach homes of the NJT executives can't be cheap either