A lots of people, particularly those who live in the northern latitudes of the US, tend to think of a beach vacation as always taking place when there is a snap to the air and snow on the ground. It is a natural response after all and the thoughts of running in on the beach with sand in your toes and the warm sun on your shoulders appeals to many. It's a fact that there are a lot of beach vacation destinations available during those truly cold winter months up in the northern states. It is interesting to note that beach vacations, typically between Thanksgiving through Memorial Day, at Florida, Texas and Mississippi beaches are the most expensive due to the "snowbird" traffic influx seen there. The prices of everything from vacation towels to swim suits at these beach resort locations are much higher during this time of the year than during the off season.
The thing to remember is that the beaches are there all year long, so catching a time when the mad rush to get warm and recapture the summer can be had even in December. Think of the Holidays like Christmas in December and a nice warm beach with lights as a fun get away. Of note is that prices for everything are generally lower if you try to time your vacations during months that might not be the most traveled during the winter season.
Hotel stays will be cheaper, eating out will be less expensive, and show tickets will be less too. There's a reason for all this and it is really simple. Most people think of summertime to go to these places and those people will pay much more than even the snowbirds coming down for some warmth. This huge surge in tourism can be boost to the local economy and they understand that it is temporary, so they jack the prices up to even out the rest of the year.
But hold the horses! Won't it be cold even there during the middle of winter? Yes and no. It will be cooler to the locals because they are acclimated to their local weather, but to someone fro Michigan, 60 degree weather in middle of winter is like a sauna.
The best route to take during the winter months to your winter get away is a train if they have routes to get you there. If not then consider the train coupled with the bus. There are no real restrictions on baggage like airplanes and the ride is much more pleasant.