From the sounds of it this is your first visit to the Cayes? I've never rented on AC so can't comment about that but the best advice I could give anyone planning a prolonged stay on Caye Caulker is don't sign on to anything long term until you get there - unless you already know the accommodations involved and have explored it all before. Find a room for 2 weeks or a month. From there you can journey to Corozal and Ambergris Caye, have a look around and see if that agrees with you more. Really, figure out if CC is what you are looking for, and if it is you should have no trouble finding great long-term accoms, hopefully Sharyn would agree. It's that kind of place.
I realise there are logistical issues involved in packing up your life and trying something new, but if it were me I'd want to find the place I wanted to start my retirement then find a place to live there instead of commiting to something based on cost before getting there. Just my thoughts.