Ambergris Caye is a great place, especially for relaxing and food and drink but those who just visit Ambergris Caye are seeing only a tiny part of Belize. Ambergris Caye is an island smaller than Barbados, whereas mainland Belize is about the size of Massachusetts.
That goes double for real estate. There's a tremendous variety of property options on the mainland, from beachfront lots to small farms to homes in all prices ranges.
I think if you're serious about looking at property in Belize, you'd probably want to visit San Pedro and also spend time in Cayo, Corozal, Placencia and maybe PG areas.
For info on the mainland, you might see my Belize First Guide to Mainland Belize (available from Amazon.com) and for info on buying, investing, or retiring in Belize my new book, Adaptor Kit: Belize, will be out from Avalon in the summer. I also did the update on the new Fodor's Guide.
Belize First Magazine http://wwww.turq.com/belizefirst/