Unless you're a HUGE air hog, there's no real rason to use doubles. I'm a bit of an air hog, and even I don't have any trouble doing the cenote tours on a single AL80, following the rule of thirds.
It's certainly possible to need more, if you're a big enough air hog. Last week in Cozumel, we dove with twins from the UK who managed to blow through their air in 20 minutes. I stayed down 44 and had 1000PSI when I got back on the boat. But frankly, their skills were so lacking that I know our guide (Alvaro from AlwaysDiving.com) would not take them in the cenotes, and I doubt anbody reputable would.