February is high-season in the Caribbean. So if you're not set on that timeframe, look at after May 1st.
Cayman is a lot of bigger stuff, always turtles - esp. near the Turtle Farm as a bunch get out when there's a hurricane - Stingrays, Stingray City is the most fun you'll have in 15', Eagle Rays, Sharks in some areas, schools of Tarpon and also small stuff like cleaner shrimp stations. A few shallow wrecks - some you can snorkel. They just sunk the Kittiwake in 58' of water - snorkelers on top, divers on the bottom.
Bonaire is mostly macro stuff - seahorses, scorpionfish, small nudibranchs (like 1/2"), squid, eels, etc. Also turtles in some areas. Curacao is very similar since they're on the same reef but there's some more interesting coral formations there that you won't find on Bonaire. And maybe a couple more beginner accessible wrecks.
Assuming you want to shore dive to save money, Bonaire or Curacao might be better options.
http://www.shorediving.com/Earth/ABC/index.htm has pictures/descriptions of the entrances etc. Notice the difference in the entry points between B & C - most of that brown stuff just offshore on Bonaire is ironshore you have to float/walk over.
Delta and USAirways have several one stop flights for under $700 - 621 on USAirways with 6-8 hr. total trip times from KC to Grand Cayman mid-Feb. But that will be offset by higher costs for food and diving, both of which are among the priciest I've seen.
You could share a 2-3 br condo - on Seven Mile Beach that would start at about $2500 - If you don't mind staying in the NW Point area farther from Georgetown and a couple miles north of SMB that price goes down to about $2000. Most will have a sleeper sofa also. If you're interested in a hotel - during Feb. most will be in the $200-500/nt+ range. Food is going to be expensive on Cayman but you'll also have nightlife and there are cheaper options, Subway, BK, Dominos etc for lunch etc. And a couple of AI resorts - Sunset House or Cobalt Coast. For us it was cheaper to get a condo, cook a few meals and eat at moderately priced places the rest of the week.
Bonaire is over $1000 next Feb. from KC and over 12 hrs. Plus about 2-3 connections. I always try to minimize the connections when possible so my dive gear gets there
with me. However Bonaire may be cheaper for diving as most resorts bundle shorediving/vehicle/lodging. Often they include 4-6 boat dives which is about all you need. You can also get a lot of good dives from the resort docks - many are on named dive sites. A lot of dive resorts on Bonaire offer quad options in condos - staying a short drive from the water (1/2 mi. or less) can be a lot cheaper also. Food is fairly high as it's imported from Curacao or Venezuela.
Another option you might look at is Curacao. Probably about the same travel time for you but they share the same reef as Bonaire but most entries are off sandy protected beaches. And there's a lot more non-diving stuff - shopping downtown, restaurants, nightclubs, casinos. There's also a lot more people - it's both the deepwater container port, oil refinery and a major cruise destination so that's a factor.
The best dive I did on either was Playa Kalki on Curacao. Some of the other sites were very similar to Bonaire. If it's of interest, you all could also do the Dolphin Dive at the Seaquarium - it's in about 40-60' - also $200pp.
Turks and Caicos will be more expensive than any of them. You might find a condo on VRBO.com on Grace Bay - which is one of the top beaches in the world. Anytime you see the Gucci store next to the Rolex store...
We only spent a couple days there on/off the Explorer so I didn't see much of it. There didn't appear to be as much to do non-diving. Diving off West Caicos and French Cay was among the best I've ever done. Flights to Provo were pretty high also.
Cozumel is a lot of deep drift diving. Often in the 80-100' range. Although it's easy diving, the task loading can sometimes overwhelm new divers. I don't go there but it's probably your cheapest option. Some friends paid about $800 last year for flights/hotel/breakfast - diving was extra. There was a $200 Orbitz discount also. They stayed in a hotel on the water a mile from town, it had a 30-40' shore dive out front and 3 diveops within walking distance. It was called Hotel Villablanca.
A good site for checking out flight options is Matrix/ITA. It's the database where Orbitz, Expedia, Kayak and many of the major airlines get their info. Google just bought them so it will probably become integrated with Google Search over time.
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