I've made the trek from NY to DC several times. The problem with traveling by train is clearly time, it can take anywhere from 3-5 hours to get into NY...and I find it pretty expensive. I think your best bet would definately be to fly, it's a lot cheaper than most people would expect. I found my last fare on Orbitz for under $130 RT. I'd check there and investigate another option. They're usually on point with that sort of stuff. Goodluck on your search.