Man, I was thinking that $2k figure was way high for just about anywhere until I started checking airfares out of Denver. United really screws y'all up don't they? I guess I won't whine about fares out of Houston anymore. The little bit of checking I did suggests the following as options...Bahamas, Cozumel, and Grand Cayman. You could also throw in Belize, Cayman Brac, Honduras, and Bonaire, but those four would probably be pushing the $2k envelope by the time you factor in taxes, shopping, tips, snacks, and any gear rental you made need to do. Of those three, GC is probably the easiest diving for beginners (only because the currents in Coz can sometimes bother divers with less than perfect buoyancy and attitude control underwater), Cozumel probably has the most to do other than diving and will be fairly cheap after the airfare, and the bahamas look to be the cheapest airfare, leaving you more to spend on picking a great resort.
My advice is don't book right away...Taca is about to face some more competition from Continental for flights to Roatan starting in June. Last time that happened, when Sol started flying there from Dallas, Taca offered a $149 RT fare from Houston. I would wait a few months and keep an eye out here and at scubadiving.com for airfare specials. Research resorts at several places you might want to go, and be ready to grab the airfare when it is available, and quickly follow with a resort booking. Keep in mind that while it is probably safely out of hurricane season for Roatan at that time, it is also the start of the rainy season, which can put a damper on diving, and degrade underwater vis.
One other alternative if you can change your travel dates is Sister Island Splash on Little Cayman (Little Cayman Beach Resort) and Cayman Brac (Brac Reef Beach Resort). I think it goes from early sept. to late oct, and includes some great prices for air inclusive packages. Both of those islands have diving that will spoil you for the rest of the caribbean, and the dive ops are the best and most safety minded that I have ever been out with (not a small issue if your wives are newly certified).
Hope that helps and good luck with the planning!