I have checked all the places I can and found www.flycheapol.com
the cheapest for this trip in November. Round trip from Salt Lake City $479.00. Each time you go, you need to check all you can, because the one that was the cheapest last time isn't necessarily the cheapest all the time. Last trip we used traveland.com. You never know.
Here are some of the others I tried.
latindiscounts.com intratours.com exitotravel.com hobbittravel.com
Good luck Kathy W.