Norwegian Airlines

Norwegian could be good, but as a young, flexible airline, looking a year ahead is unreliable because they do change their schedules. They will take your reservation, but if there is a change in days they fly or gateway city, you'd either have to accept it, or get a full refund back.
Second, they don't fly from all their airports every day and have been known to cancel flights. Do you have enough flexibility to fly out a couple of days later if your flight is canceled, or could you get yourself to another gateway city? Finally, you need to pay for seat selection and checking luggage with each segment, or pay the slightly higher fare to have all included.

You could also look at Icelandic where seat selection and checked bag are included. They've been around for decades and decades and are not known to cancel flights at the last minute. Or Aer Lingus. Additionally, at airports that have competition from low-cost carriers, the legacy airlines tend to lower their fares to compete with Them.

Edit: if it’s a non-stop flight, as Bob mentions, sounds like a winner, but be flexible in case the routing changes.

Norwegian has nonstop flights from Bradley (Hartford) to Edinburgh.

We also like the new Aer Lingus flight nonstop from Hartford to Dublin. Once nice feature is that you can go through US Customs and Immigration in Dublin on the way home.

Have flown Norwegian in both 2016 & 2017 with no issues at all. In '16 it was BOS-MAD, and return was Barcelona-Copenhagan-BOS; used "flex fare" which included meals and baggage for that trip and total cost each was €770. Then in '17 RT BWI-Martinique again with food and baggage for $255; they even waited for me as I sprinted to the gate in Martinique with people at the counter, security, and gate cheering me on.
Finally, in 2018, am planning on using them again to get to Copenhagan and using the ICE to get me to Hanover for CEMAT in April.
Yes, early-on they did have glitches getting there act together, however, they no have the most modern Boeing 737 extended range fleet flying. Book with confidence.

I would book but watch it carefully depending on which airport you are using. For example, last year I flew BWI to Guadeloupe, but this winter, Norwegian no longer flies out of BWI at all. That is the reason I said they are still changing things around.

We have flown in them 5 legs, and had no problem. Going east, we brought a!ong a stash of food. Going west, we sprang for their meal and snack+-airline food.
Norwegian Air Shuttle is the third largest budget air carrier in Europe, and don't overlook they can get you to most European cities after flying into their gateway cities. They are not a startup or small operation.
And the big US legacy carriers do not like that Norwegian has forced them to essentially lower their cards sometimes in half.

As more new Boeing 787's are delivered, we are seeing Norwegian branching out to new airports. Chicago is coming online in the Spring, and it is their first destination in mid-America. I am very thankful to have them keep the legacies honest on airfares.

I am committed to flying Norwegian to Martinique out of Providence in January and looking right now at flights to Norway in May. You said "East Coast" but didn't specify a city--check Providence.
Cynthia

I set up skyscanner alerts to find the best deals on flights.

How fortunate you are to be on the east coast already! I am traveling from the west coast so there's some added cost. I had been looking very often at Norwegian as an option for me to get to Europe as cheap as possible but I watched fares enough that I ended up booking British Airways for not much more. I would set up kayak.com and skyscanner.com and subscribe to Scott's Cheap Flights and look for deals.

Just took Norwegian Denver to Gatwick. Was a good experience. Flight attendants were friendly, new 787 with decent space even in economy, flights went smooth, decent entertainment options. Just be familiar with baggage restrictions. You can take a hand bag and personal item but it is limited to 10 kg between them and they did weigh them. We went with our family and did not reserve seats at extra cost and we were seated together. I would fly them again, if you do need more luggage than 10 kg be sure to pay for it ahead of time online, there is a savings.

Thank you all for the input on Norwegian Airlines and info on other possibilities
I has been very helpful