I read about a person who wanted a flight from Los Angeles to Las Vegas. She got a good price with Priceline. Only trouble was, she was routed through Phoenix and it took her all day....She could have driven it faster....
I've never been brave enough to try it after reading that.
If you have limited time, I'd be worried I'd lose a day or two with bad plane connections on each end.
If you do have extra time, consider flying into Cancun and taking the bus/water taxi down. Yes, it takes two days, but, you'll know going in what the connections are.