Fly nonstop from New York JFK to Reykjavik, Iceland for $299 roundtrip on Delta starting this July through April of 2019.
Flights are available daily and even a tad bit cheaper in fall and winter months coming in at $289 roundtrip. If you can't find dates on Delta that fit your schedule, Icelandair is also matching this price. Unfortunately, these book into Basic Economy, which means checked baggage will cost extra. Regular sized carry-on bags are included, and that's all you'll really need for a quick summer getaway to Iceland.
Searching on Delta's website, I found seats departing JFK on Saturday, July 28, and returning from KEF on Wednesday, August 1, 2018.
If you need a place to stay in Iceland, here's a list of available accommodation for the sample dates on Hotelwatchdog.