WOW Air has brought back their $99 one-way fares from Boston to Iceland. The cheapest return flights are $164.39 making the roundtrip total $263.39 per person.
This is not the first time they have run this sale and these deals have been very popular in the past. Keep in mind WOW is a low cost carrier, so be prepared to pay for bags, seats and more.
You can search for prices by using the WOW Air fare calendar. Flights are also searchable on Google Flights, however they show up as $10 more, but are correctly priced when you click through to the WOW Air website.
For more info about dates and fees, see this View from the Wing post