USA3000, the quasi-charter flight operation that sells directly to the public, offers a sale to warm destinations for travel during winter's coldest days.
A sampling of the routes on sale (one-way fares, taxes and fees extra):
St. Louis to Ft. Myers, Florida: $69.99
Chicago to Cancun, Mexico: $99.99
Cleveland to Punta Cana, Dominican Republic: $99.99
Chicago to Montego Bay, Jamaica: $129.99
Detroit to Puerto Vallarta, Mexico: $139.99
Yes, these fares are being offered for departures in December, January, and beyond, but availability is limited. Finding the lowest "starting at" prices can be a challenge but not impossible. On the Chicago-Cancun route, for example, we were able to find several dates available at $99.99 each for departures in January. If the cheapest price isn't available, the next best price doesn't cost all that much more: Again on the Chicago-Cancun scenario, there were plenty of dates offered at a rate of $129.99 each way, which is still pretty good.
For more details, a list of sale routes, and bookings, check out USA3000's website.
Never heard of USA3000? Not long ago, we profiled the airline, along with a handful of other small interesting upstart carriers, in our story, "Flying Under the Radar."