Unfortunately there usually aren't any good deals anymore without an advance purchase. I use itasoftware.com (click on search for airfares using QPX) and it'll quickly tell you what all the fares are on all the different airlines for your dates and cities. Not sure exactly where in Texas you are going but it looks like to get a decent fare from LAS to DFW ($218 roundtrip) you need to book 14 days in advance.