From your list, I only have experience with Grand Cayman. Yes, the exchange rate hurts. Plus, like any other island, everything is brought in my ship. It's pricey, but we continue to go there because the diving is great, everything is relatively nice and convenient, people are nice, English is the local language. If you're trying to save a buck or two, buy groceries, eat breakfast and lunch in your condo, even two or three evening meals in the condo if possible. This will save a bunch. If you're still tight, don't boat dive, shore dive. There's lots of good shore diving on Grand Cayman: Cobalt Coast, Turtle Reef, Light House, Devil's Grotto, ... just to name a few.
One year we hired a local dive guide for a couple of days to show us where some of the lesser known shore entries were. It paid dividends for several years. Some development and hurricane damage has taken away a few spots, but renting tanks is a lot cheaper than paying for a boat dive. But if you've never been, don't skip boat dives if you can afford it.