Hi Dutchie,
I'm in Houston. While I can't comment on the charter flights, our "big airline" flights don't seem to be much more reasonable than other parts of the country. Haven't figured that out yet, since many flights stop here on the way back. We usually find the best deal with Continental - I think $330-350 is usually the best that can be found, and that's with Tuesday/Wednesday dates. I was looking for flights for late May and they're over $400 right now. However, we did fly last November for only $350 each. But here's the good news - you can fly roundtrip for as little as 35,000 reward miles. Would you be able to transfer some of your reward miles to a Continental One Pass account (free to set up)? I know you can transfer from American Express and some related airlines. If you could get to Houston for 118,000, then Cancun for 35,000 that would be considerably less than the 330K direct.
Another option to consider would be Dallas. I think the best flights from there are probably with American, since that's their hub (as Houston is for Continental). Also, from reading the forum, it seems flights from Minnesota are incredibly cheap!
Good luck!
Buzz
P.S. I should mention that Continental is really a great airline (no, I don't work there)
. They have a GREAT on-time record. It's very very rare that we've encountered any problems with our flights. And they also taxi right up to the gate - no buses.