Check out Amtrak for Lafayette to San Antonio, maybe thats the way to go?
Expedia is good.
www.expedia.com
There's also Orbitz. (I've never used it, but have heard a few good things about them.)
Cheap Travel, Flights, Hotels, Vacations, Car Rentals, Cruise, Activities on Orbitz
You may want to check and see if Southwest Airlines is at both airport. If so, that would be a good airline to use because they're usually cheap.