A few clarifications .....
Granite counters - Jerry Wilken of Architectural Accents in Ladyville does an excellent job of granite installation. Check with him for selection and cost.
A custom-built 20' X 40' pool with substantial deck space will cost from $40-50,000 US depending on materials and systems chosen.
Construction costs per sq. foot are calculated differently from builder to builder here. Some take an overall footprint (including covered decks) and give you an all inclusive estimate for a home with fixtures and cabinets. Others have one price for interior, one for decks, one for cistern and a la carte for cabinets, toilets etc.
A home with a stand-alone water system will run more than one without.
For a first-world quality home, the all-inclusive style cost (decks, cistern, toilets etc) built to deal with tropical weather (including hurricane) the ballpark construction cost is $125 - 160 US a square foot. Properly planned, with carefully selected materials you can build for less, but as Josh notes you can easily spend a lot more if you want to.
The cost to insure a wood structure is about 3 times that of a concrete one, and insurance on wood homes in the cayes is not so easy to get these days.
Tim mentions "north side" costs being higher than "south" due to transportation. This is advice about Ambergris Caye. I'd like to elaborate on that a bit because there are a host of variables. The island is 26 miles long. San Pedro sits about 5 miles north of the southern tip. Ergo - the "north side is more than 20 miles of island. Conditions on those 20 miles vary greatly. Firstly - pretty much all building materials come to the island by barge. If you are getting sufficient materials, you may find that the barge from the mainland can call directly at your building site and deliver. No need for the extra cost to offload on island and truck to site. This assumes that you are building in an area close to the water and have an offload berm somewhat nearby.
On the other hand, if for example, if you are building 20 miles north, you will find that the reef meets the land, that no barge can get up that way, and that your materials will have to come in smaller loads via the back or outside the reef.
As you can see, the info on transportation is VERY location-specific. Tim's advice is about Ambergris Caye, Danes knows Caye Caulker well - and the information on this would be quite different for a mainland location.
I notice a blog in progress by an new resident building a home about a mile north of the bridge. You may wish to follow this story .....
Edited by Diane Campbell (01/20/13 09:07 AM)