Greetings All:

Just remember the chance of getting  paid employment  in Belize is close to ZERO, so If you feel you need to add to your benefits to be able to live comfortably you need to have some form of self employment, with a legal self employed work permit, or external, Possibly online paying position.
If you want to live comfortably you have to decide what you need for  your comfort . If you wish to eat only american branded foods, Have all  your fruits and vegetables available all year round and like to drink nice wine with all your evening meals then you will need a good income.
In Belize  fruits and vegetables that grow here are seasonal  for instance Avocados are not available out of season. If things do not grow here then they will be more expensive than in the US as they will all be imported.  Chicken is the most common meat in Belize prices are good and the quality of the meat is good. also plenty of pork and Bacon, Many complain about the quality of the beef ( comparing to shoe leather I believe) but if you are a good cook and treat it accordingly it is a well flavoured meat. Fish and seafood are good but where ever you live you may have to look and ask around for the best retailers, or market stall holders.
To be fair one contributer to this forum has always detested the beef , been affronted at the lack of ready made pie shells, and the  high cost of imported wine and Mushrooms, back to the time when he still lived in Belize.
Housing costs again depends on your expectations, simple houses rent or buying will cost less than a concrete McMansion. Beach property will cost more than inland village property. Cayes property will be the most expensive.

Electricity is often Quoted  as  expensive but  again depends on how much you use, and what the cost is in your present Locality outside of Belize.  If you NEED 24 hour air conditioning year round then you will have a very high bills. If you are happy with fans for much of the time with aircon as a short boost from time to time then much more manageable bills.  Ideally a home using  solar energy will be virtually bill free after installation  costs.  AND You will not have winter heating bills to contend with.
Mains water and sewerage  is only available in larger towns and cities, Most other homes will use water catchment tanks and septic systems.  As we are in the most other homes category I have no idea if the Water and Sewerage charges are expensive or not.
Transportation, well depending on where you decide to live, busses are cheap bone shakers,  If in  town/city taxis are cheap, good idea to get to know a regular cab driver, they can be fonts of local knowledge. 
Vehicles to buy are expensive for what you can get.  If you decide to buy a vehicle it is Essential you quickly find a car mechanic that knows that make of vehicle so  you can  have some faith  or trust, he knows what he is doing, you will need one sooner or later, just kidding, it WILL be sooner.     Belize roads eat cars. Gas is about $5us per gallon,  at the moment, but Belize is small so probably not driving nearly as many miles anyway. 

From time to time folks  put up shopping lists for direct comparison costs, only useful if it is the sort of stuff you would buy in either country, one showed an  incredibly high price for Velveeta cheese products n Belize compared to Canada or the USA, I would not buy it in ANY place so to me the comparison not useful. Nescafe Instant Coffee is cheaper in Belize than California, funny as both import it from Mexico.
Also for some reason the quality of the toilet paper seems to get people excited, again Imported things will cost more, so if you must only have the softest triple ply US brands they will cost a lot more than the locally produced brand. One of the very few things actually manufactured within Belize  is Rose Toilet paper, and expats are still willing to pay 3  or 4 times as much  for not supporting this local Business as they think it's  product is too rough for the tush.
Now just wait a while and you will get advice to go any where else but Belize from lots of ex expats or some who are presently not happy with the choices they made so it must be the countries fault.
Heads up Belize used to be different,  some want it to go back to what it was then, quieter less crowded, because obviously no other place has changed in the last 20 years or so.

Exilant info Terrific:

The only thing I can add is water and electricity cost ($BZ) in Placencia.

Water is $10/month from 0-1000 gallons. And a penny a gallon over that. We seldom use more than the basic 1,000 gallons except a few dry times when I hand watered the shrubs and trees in the yard several times a week.

Electricity is not that expensive compared to what is typical in Texas. We do not have A/C yet, relying on ceiling fans, open windows with sea breezes much of the time. Highest bill was $84 for 238 KW back in march.