Doing Jet Blue one way SDQ-FLL $120 something this month.
http://tinyurl.com/28hlwye
<a href="http://www.flickr.com/photos/34557194@N07/5331085422/" title="spirit9dollars by socuban, on Flickr"><img src="http://farm6.static.flickr.com/5123/5331085422_1e5befbf0e.jpg" width="443" height="500" alt="spirit9dollars" /></a>
Go on Spirit's web site (or any other airline for that matter) and book the trip both ways for the same dates..any dates. If the point of origin for a round trip is in the D.R. and the destination is in the U.S. the fares are markedly higher than the other way around.