Originally Posted by
Often1
You might also want to look into taking Amtrak between Washington and Newark.
The cheapest option would likely be to take the original flight DCA-EWR, then take the train back to Washington. Then postpone EWR-ZRH to a later date. That would likely avoid having to re-fare the entire trip as would occur if staying more than 24 hours in IAD/DCA. Of course, whether the extra time makes sense is only something the OP can decide...
And from the school of crazy airfares, United currently has a 49 cent base fare from the ZRH to EWR. Of course, that's basic economy, and ignores the $300 in "Carrier-imposed surcharge", but still...