If cheap domestic flights aren't getting you excited, booking a trip to Scandinavia should do the trick.
Scott's Cheap Flights found super cheap round-trip flights from major airports across the U.S. to Stockholm for travel from September through March of next year starting at $302 — but it gets better. T+L found flights from cities including New York starting at $296.
Cheap flights are also available from Chicago, Denver, Las Vegas, Miami, and Washington D.C. If none of those are your home airport, check fares to Stockholm anyway — you might find a deal if you're flexible on travel dates.
Some of the cheapest fares are on WOW Air (no surprise there), but other airlines including United, Icelandair, Swiss, and Air Canada also have cheap fares available.