Maybe this one would work for you Aaron, if you could convince people to leave on Christmas Day. It leaves about $962/person in the budget, or about $274/night for each couple to share a room at an all inclusive resort.
Christmas to New Years Day flight to Cancun - $438 roundtrip after taxes
$438 roundtrip after taxes isn't the cheapest flight I've ever seen to Cancun, but the important factor here is that it's a Christmas/New Year's flight.
All the time, people understandably want to know if there are deals to be had around Christmas or New Year's, and I try to explain to them that it's unbelievably rare to see a deal to *anywhere* at Christmas, never mind the infinitesimally low odds that a great deal will arise to the one destination they have in mind.
It's the one or two weeks of the year where virtually everyone has enough holiday time to take a holiday together, which means demand is exponentially increased, while supply remains exactly the same. Anyone that's taken Econ 101 can tell you what that means. It's the invisible hand at work, keeping prices sky high all around.
So here we have a flight that in the context of any other date range wouldn't be overly extraordinary. It would be a very good price mind you, ever so slightly below the usual bottom price from Calgary to Cancun of around $450-$500ish. But in the context of Christmas, it shines much brighter.
To find it, try this search:
http://www.kayak.com/flights/#YYC-CU...-flexible-1day
screenshot:
Let's note the other airlines, and what they're charging for Christmas flights, roundtrip after taxes:
Continental: $875
Air Canada: $879
United: $937
Westjet: $961
Delta: $1523
And here we have Air Transat, offering up a flight for almost exactly 50% of the next cheapest airline.
To note, if you click through from Kayak to Air Transat's site you'll find that booking through AirTransat.ca is going to cost $1189! So instead, click through to Expedia, or Travelocity, or Orbitz who are all displaying it at $430ish.
Why is that? It just happens sometimes, and it's definitely not the first time I've seen it happen with Air Transat and the major booking sites. In fact, I often see the reverse as well, where AirTransat.ca is cheaper than the major booking sites. It usually pays to try both.
I will also note that this Christmas flight is just an example. Air Transat seems to have dropped their flights throughout November, December, January, February, and March. Try a 3 day flexible date search on Kayak to find them.
November search example:
http://www.kayak.com/flights/#YYC-CU...-flexible-1day
January:
http://www.kayak.com/flights/#YYC-CU...-flexible-1day
February:
http://www.kayak.com/flights/#YYC-CU...-flexible-1day
March:
http://www.kayak.com/flights/#YYC-CU...-flexible-1day
April:
http://www.kayak.com/flights/#YYC-CU...-flexible-1day
The other nice thing about these flights is that they're all direct each way.