There are nominal services charges ($5-$10) charged by Travelocity, Hotwire, Orbitz, etc. You can use those sites to determine which of the major airlines have the cheapest rates. Then go to Southwest.com, Jetblue.com, etc. to check the discount airlines' rates. If the major airlines have cheaper rates, you can go directly to their site and purchase the fare you located on the search engine, but save the service charge.