Funny thing is, we managed it for Hawaii a couple of years ago. You get some frequent flyer miles, pay for a ticket and half of another like that, limit the baggage and you can drop the per ticket cost down. Then, airbnb is a lifesaver when it comes to finding a space big enough for three couples.

After that, we bought the Costco Oahu Go cards, where you get all kinds of things for well off the individual entry fees, including the best package at the Polynesian Cultural Center (luau, show, and all the rest). By the time you go there and Pearl Harbor and see a couple things there, the GoCard has paid for itself and you still have around two dozen other places you can go. We actually weren't able to see everything. :)

I've checked into flights and airbnb in the Cancun area, and depending on the time of year and the airline, we could probably make it happen for an arm and maybe an ear. :)