I think a month diving in the Bahamas would be pretty expensive. Food is extremely high and a decent rental has to be $3K or more for the month - around $100/nt. seems the typical
starting price on vrbo.com. If you want to be anywhere near Cable Beach - it's closer to $5K.
Actually the most reasonable expense is probably the AOW class - it's $210 at Coves. But then you've got the rest of the 3-1/2 weeks of boat diving since there's no shore diving in the Bahamas. Dive prices are fixed at around 2/$115 so that's a huge chunk of cash if you plan to do any.
For that kind of outlay there are some less expensive dive resorts you could stay at. Cocoview on Roatan is $1500 wk. all inclusive. And has one of the few shore dives on Roatan. Roatan's West End is pretty reasonable also - it is kind of a jello shot place closer to the weekends though. Dives are 10/$300, night dives are $40 and AOW thru Coconut Tree (one example) is $280. Flights are a little more but well under $1K - although maybe not this close to Feb. You should be able to get a 1BR apt. with kitchen for in the $50/nt. range - check Coconut Tree Cabins or Posada Arco Iris. Both are in town and you don't need/want a car. There's also two hostels - Chillies even has Native Sons on-site for diving. Food is street vendors on up.
Cabs are cheap if you need to get somewhere else so your inter-island travel expense is $25 from the airport. CTD has a good summary page of what's in/near the West End here:
Roatán, West End | Scuba Diving | Roatan, Bay Islands, Honduras | PADI
One gotcha about the West End is that the north side may shut down for weather for a few days during the winter when a storm blows in. I think Feb. is past most of that. The bigger operators have the resources to shuttle you to the south side which is always open. You might also consider doing both - 2-3 wks. in the West End then a week at Cocoview or Reef House Resort to dive both sides of Roatan - they're different - However you may not be able to get into Cocoview this late - it's pretty popular.
I second InstaGator's idea also - Bonaire or Curacao. Maybe split the time between them - flights between the two islands are $100 r/t mid-week. It seems to always be cheaper to fly into Curacao then continue on to Bonaire also. The only downside with either place is you'll need a car to take advantage of all the good shore diving so that's going to be about $1500 more for the month. At shore dive sites on both islands we've been asked if we need/want a buddy.
If you're willing to give up staying waterfront there are some good deals on either island. Look at places like Coco Palm Garden or Lagoen Hill on Bonaire or some of the not-waterfront properties in Kralendijk - most are just a block or two inland. The Kralendijk properties put you walking distance from many shops/markets/restaurants and all the nightlife on Bonaire. Also check vrbo.com and
Sunbelt Realty - both have longer term rentals. Some in town, some (in Belnem) five mins. from town - the ones in Sabadeco are farther north.
I don't know any of the less expensive places on Curacao but there are some. We stayed in Lagun at My Dream Apts. for $65 nt. but I don't recommend it for a single - first of all you may be the only one there, second it's about 30mins. to town from there. There isn't even a market nearby except for one toku - small roadside shop.
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