Airfare Watchdog

Farealert@airfarewatchdog.com    (double check this) is a terrific site where you can sign up and have rock bottom (sometimes) fares emailed to you.   I get them twice a week.   You sign up and give them your nearest airport.. and they send you low fares.  

Spirit Airlines, they fly out of Detroit.... if you join their $9 fare club  ($39  I believe/year) and you're lucky.. you can fly one way for $9.  I've found the cheap fares ONE way.. but never been able to snag one both ways.  I'd go almost anywhere for an eighteen  dollar flight.  Maybe not Mexico...