Anything to do with water has always relaxed me. Sitting by the Chesapeake Bay (rather cold this time of year!), driving down the Outer Banks, spending a long weekend in Sea Island, GA (FANTASTIC marshland on the Intercoastal Waterway) on one side of the island, Atlantic Ocean on the other side.
I don't know what to tell you regarding water. There are tons of 4-day cruises (last minute) on Expedia where you can save up to 70 percent. You may not get the cabin of your dreams, but you'll get to be on warm, sunny beaches. This time of year, south Florida is warm. I lived in Miami in the late 80's and it was WARM this time of year. The Florida Keys are spectacularly beautiful and there are plenty of inexpensive places to hang out.
I hope those suggestions are somewhat realistic. If you're not a water person, I'm sure some mountain people will be along shortly with their suggestions ...