Agree with the Caveman.
$400 US for a furnished cabin in Caye Caulker is a bit unrealistic.
It is important to note that real estate (including rentals) on Caye Caulker is far more expensive than on the mainland.
On the mainland, you can get a very nice rental for $400 US, on the islands - not so much! It is a matter of supply & demand, plus the quality of life (of course).