Via View From the Wing, you can fly from 3 East Coast airports to Dublin, Shannon, Belfast, and Edinburgh in coach for $65 one-way. And you can even get a pretty cheap return flight!
I found flights from New York (Newburgh-Stewart) to Edinburgh, Scotland, for $161 round-trip in coach for travel on November 13, 2017, to November 21, 2017. These fares are valid for select dates between June 15, 2017, and December 31, 2017.
Here are the details. And how to search for deals from your city!