What do you want the $1250 to cover? Air, hotel, food, drink, diving? If so, that will be hard to do at any decent diving destination other than Cozumel. At lots of good destinations, like Belize, it's hard to do the air for less than $800-$900. Coz is one of the best deals going. You aren't restricted to the AIs at the southern end of the island, either. You can put together good deals at lots of hotels in or near town, where it is easier to get into town to have fun (which sounds like a good idea for a guys' trip) and get picked up by more dive operators. I have had good luck with deals from Apple Vacations at the Fiesta Americana, which is a decent enough place. FA has an all-inclusive option and it doesn't add much to the price, so if you want to go to town for dinner (which is a great idea), you don't feel like you are wasting money. We can get pacakges for air, airport transfers, hotel, and AI (including alcohol) for under $1000 per person from Detroit. You should be abe to get similar prices from almost any major airport.
