I am going to suggest something completely different but it might be an option for you. One of the cheapest places to get a lot of good diving in the western hemisphere is the Dutch island of Bonaire. It's not liveaboard diving it is primarily shore diving, and Bonaire isn't necessarily a cheap or easy place to get to or live but there are less expensive venues.
Right now the all-inclusive Plaza Resort Bonaire is offering a one-week $888 per diver special, that includes your accommodations, food, alcohol, and unlimited shore diving including Nitrox, transfers, taxes, and service charges. If you can find reasonably-priced airfare to Bonaire this might work for you.
Bonaire is very good diving and a unique place to visit - the entire island is all about diving freedom. It's a lot of fun! To experience the best of Bonaire it is advisable to rent a car or truck and that will add on some expense, but you can grab some unlimited tanks at the resort dive shop and head off down the road to find many, many shore dive locations. It is also an interesting place to explore IMO.
There is also an annual fee of $25 to dive in the marine park and a $9 departure tax to leave the country but other than that and the truck rental/fuel, most of your expenses are covered by the Plaza Resort package. But be aware that there are persistent problems with petty thievery on Bonaire and you cannot leave anything of value in your truck while you are out diving.
I have been to Bonaire several times but I have never stayed at the Plaza Resort and I have read mixed reviews about it. Below is information about the current special, I know it is not what you've asked for but I am suggesting it as a possible alternative that might work for your budget, good luck!
Plaza Resort Bonaire
20% OFF includes 7 night junior suite laguna view accommodations, 6 days of unlimited shore diving, all meals, snacks and beverages including house brand alcohol, free WiFi, scheduled entertainment, use of non-motorized watersports, airport transfers, hotel tax, and service charges. Travel through 12/18/15. Add on 6 days of 1-tank boat dives for $140 per person. From $888 per person double diver
https://www.plazaresortbonaire.eu/en
---------- Post added April 12th, 2015 at 07:00 AM ----------
Oh! Then I have been on lots of safari dive trips, thanks!
---------- Post added April 12th, 2015 at 07:32 AM ----------
Another possible land-based option for you is the Brac Reef Beach Resort on the British island of Cayman Brac.
No one would call the Caymans a cheap destination but I have taken 3 dive trips to the BRBR and I think it is a terrific bargain.
Below is their current $1590 special and it covers absolutely everything except your airfare and tips for the dive operation. You can add on a couple of night dives for an extra charge if desired.
You won't need to rent a car and the hotel provides free bicycles so that you can explore. It's an all-inclusive, small, diver-dedicated resort and the food is excellent IMO. The island is small, safe, beautiful, clean and the people are friendly. You can drink the water and eat the food without concern and the diving is very good.
At lot depends on the costs of airfare, but the Caymans are usually cheaper and easier to get to then Bonaire in my experience. I just checked the Cayman Air website and found roundtrip flights from Tampa Florida to Cayman Brac for $230 per person and that's not bad. Other airlines fly to Grand Cayman so you might get a better deal, but you will need to fly Cayman Air to get from Grand Cayman to Brac. But most major airlines will book you through to Brac because they have arrangements with CA.
Cayman Islands All Inclusive | Cayman Islands Vacations
CLEARLY CAYMAN PACKAGE
Valid for travel January 3 – December 16 2015
7 Nights Accommodations
Breakfast, Lunch & Dinner
Three Drinks Nightly
17 Boat Dives
Airport Ground Transfers
Free Welcome Rum Punch
Hotel Taxes & Service Fees
US $1590 per person double occupancy
---------- Post added April 12th, 2015 at 08:15 AM ----------
One last comment and then I will stop offering suggestions! You've asked a couple of times about last-minute liveaboard dive specials. I have never been to the Galapagos so I'm not familiar with the discounts you have experienced there, but I have been diving for more than 30 years and I have only gotten 2 last minute liveaboard specials in all that time (Bahamas and Hawaii) and we were lucky to find them at a time that we could use them.
In both cases, the boats had been charted by a dive club at a good price and then a couple of divers dropped out at the last minute. The other divers were desperately looking for someone to take the empty spots so they could still go on their trip as planned. But those were very rare and uncertain situations and difficult to find. I'm not saying that it's impossible to get a last minute liveaboard deal, but it is unusual and you shouldn't count on it. Sometimes dive operations and liveaboards cut their prices for low season. You will be traveling in early Summer and that is not the high season in Florida, Bahamas, and Caribbean, but it is not the low season either (August through October - hurricane season - is the low season).
I am sure that there are other opinions but I think that your best choices close to your budget are the Blackbeard's liveaboard out of Nassau (camping at sea in dormitory accomodations) or find an all-inclusive dive resort with land-based diving. Of the suggestions above, I think the BRBR on Cayman Brac is your best option, just my opinion.
There are other cheaper all-inclusive dive resorts in other locations but often they are difficult and expensive to get there and the diving/resort/food may not be as nice in my experience. Some of the really big all-inclusive luxury resorts also offer price specials that include scuba, but they are not diver-dedicated resorts and you may find yourself on a cattle boat with a lot of inexperienced divers. Good luck! Kathy