Hey Don, how about Tucson to Cancun? What's your best deal there?
Or PHX, I could leave from there too if it's cheaper...
Could you drive to Austin Texas...?
It's funny how flying from Austin thru Phoenix can be cheaper than originating in Phoenix. Just depends on who is competing with whom. I looked at Sidestep.com/Kayak.com (same site, different appearance) as it is pretty good at checking all possibilities without jerking the shopper around, then usually allowing you to book at the airline site that will jerk you around if you shop there first.
I really don't see any point in the itineraries that make you change planes twice on the way so let's skip those starting at $498. I also avoid overnight connections that involve long hours in an airport, altho flying overnight is ok.
US Airways: Tuscon to Cancun for $531 RT - 1 change in Phoenix. 7am departure into CUN at 3 with time change; 4pm return into TUS before 9 - probly your best option.
Air Trans: Phoenix to Cancun for $597 RT - 1 change, overnight flying but not bad. Leave on the 11th
Frontier: Phoenix to Cancun for $621 RT - 1 change
US Air: Phoenix to Cancun for $687 RT - Non-stop :cool2:
American Air really tries to get passengers to overnight in DFW - which is not much fun and ruins fare savings.
Tuscon to Cozumel is not easy, but these flight beat driving thru Mexico anyway.

It's worth it even thru Cancun. Take a look at Sidestep and see if I missed anything...?
I've done 20 hour trips from my house to Coz hotel after an afternoon at a Dentist on the way, saving enough on the Dentist to pay for the trip, and still made the 8am boat, but you don't need to do that.