I checked
http://www.airtran.com/
$244 round trip washington / Tampa
This is a nice airline, a real up and commer.
No must buy 7 days in advance, one way fares are not a big gouge.
see ExPat's search for airline tickets from DC. Only $240.
http://www.freerepublic.com/focus/f-news/1352657/posts?page=3753#3753