@Kharon. I couldn't agree more with you. In general, over the past 20 years the quality of Caribbean diving has gone into the toilet. Belize is a mess. Costs are through the roof. After 5 visits to Bonaire since 1996, I have seen a serious decline. Where are the big groupers? For my wife and daughter-in-law, the snorkelling is a trip over rubble and fire coral. But it remains the best close to the US. If you go for 2 weeks or longer you should consider beyond the Caribbean --- well beyond.
My current choice would be Sulawesi in Indonesia; perhaps NE Bali if you need more night-life and have to have shore diving. $1900 (= €120 per night) will get you 12 nights accommodation, 3 boat dives per day, all you meals and non-alc beverages, and you will have about €250 left over for the extra flight cost. For that you will get +4x the fish species density and infinitely better corals than on Bonaire. Beware - alcohol is expensive. The Siladen island west reef has the best instantly available snorkling that I have yet come across - you walk across sand to a channel leading 10m to the wall. Otherwise the Philipines, if you can deal with an occasional leech.
But regarding your detail. Yup, Gran Cayman prices are wicked. Taxes are high and exchange rate is crabby. Overrated fish life. Really good (I mean REALLY good snorkelling places can be counted on one hand). Used to go there but then found better fish, corals (2002-2006) and value in Cozumel. Roatan has prices everywhere from Mayoka at €434 per night to Coconut Tree Cabins where I stayed for absolute peanuts (nice deck; good airco; don't plan on cooking a 4-course meal in the kitchen, and don't go in May or the sand flies will carry you away). OUCH - $3800 per fortnight!! Where was this? At Anthony's? Roatan annual dive fee $10. Roatan rental equipment $5 per day. Bonaire - $24+.
Bonaire charges $5.50 per tourist per day. 4 peeps and that is $22 to add onto the $120 for the apartment. (= almost 20% extra). Snorklers tag costs $15. Free most other places. Then add the theme of this thread.
So, you see, you were wrong, Kharon. Or overly sarcastic at best. I don't need excuses. I have ample experience not to need them. And if you have to search for the good snorkelling spots ..... say no more.