Where do you find the lowest prices for trips

I don't know about the lowest price, but I recently went with bayadventures.com. 7 nights at plaza las glorias, five two tank boat dives with Dive Paradise, and airline tickets from LA was about $1,100. If I went back, I'd actually stay on the mainland at Playa del Carmen...much nicer place. I'd take the ferry to Cozumel a few times to dive. The ferry is only $6.50 one way and takes about an hour....But if you are a serious diver, dive 3 times a day, and don't care about ambience, stay in cozumel... just MHO...