Dandy Don, I haven't tried the Matrix ITA software, as it doesn't work on my iPad (which is where I do most of my searching). Does it pick up routes and fares for ALL Airlines, including Southwest, AirTrans, and Sun Country, which normally only sell through their own websites?
ALSO, you have to be careful comparing fares; although all Airlines are now required to report gross fares, including all taxes and fees, the extra baggage fees differ from airline to airline. I just checked Airtrans, to see what a RT from San Antonio to Cancun would cost me in June (it varies by date, but dates I checked, June 13 - June 20, low RT total was about $525), and I noticed that AirTrans charges for all checked luggage - $20 for first bag, $25 for second bag. Sun Country, out of DFW, USED to give you first bag free on international routes, but NOW charges for both First ($20 online, $25 at airport) and second ($30 online, $35 at airport) bags. American Airlines, for same dates in June, costs $578 for RT to Cozumel vs. $515 on Sun Country, but AA gives you first checked bag free (on flights to/from Mexico), $40 for second bag. SO, a traveler with just one checked bag each way pays $578 on AA vs. $555 on Sun Country. With 2 checked bags, that traveler pays $658 on AA vs. $615 on Sun Country.