There are no rules set in stone concerning which websites are the cheapest or which airlines are the most affordable. No such thing. While WOW Air and Aer Lingus might be one of the cheapest international airlines from the east coast to Western and Northern Europe you certainly have to compare the prices with other airlines; you just never know who is running a promotion. In Europe check out RyanAir, Easyjet, AirBaltic, WizzAir, Volotea and Vueling, where tickets start from 6 Euro one way with taxes and fees included.
Keep in mind that Wow Air charges a service fee if you don’t book directly with them, which is $26 per flight leg. Seat selection is anywhere between $9-48 per flight leg. Checked baggage is $48 if prepaid online, $68 if paid at the airport. Hand luggage is free up to 11 pounds (5 kg) but over the free allowance it will cost you $38 if prepaid online and $48 if paid at the airport. This is very typical for European airlines, they try to off-set the low costs but if you are a smart traveler you can still save money by not selecting a seat (let the airline choose for you) and packing light.
Certain airlines charge you for tickets purchased over the phone so do it online, no big deal. Curbside check-in can also cost you a few bucks so line up inside the terminal or check-in online up to 24 hours before departure, you can even print your own luggage tag!
Take your headset with you, most likely the airline will charge you for it. If your flight is long you will need one, if not for onboard entertainment, to cancel the noise around you.
Food on flights: Forget free food on domestic flights within the USA and Europe, you are lucky if you get a cookie or a whole peanut, and unfortunately the same goes on international flights shorter than 6 hours, unless you are flying on first class. The flight attendants hand you a “menu” with a small and not-so-great selection of food items, never mind healthy. I say bring your own food or get a meal to go at the airport.
We flew from Paris to Washington on Iceland Air, changing in Reykjavik. The first leg was about 4 hours, the second was 6 and we had to beg for water. Luckily we purchased breakfast in Paris and bought some meals to go at the connecting airport so we managed the 10 hour flight. On a side note: while the Reykjavik airport is very modern and clean, it is the smallest I have ever seen which gets super crowded in the summer months due to the short tourist season. Lines were long at the bathrooms and food court; I tend to think they are one of the most expensive airports in terms of food costs due to the cold climate on this northern island where they export goods.