Hi conga :
I go to cuba every year, and I am positive that the usual price, especially in high season, its not 15 dollars a night. Its a matter of bussiness cost/benefit , if they charge that, they cant pay the license to the cuban government and have a profit.
Most cubans dont have the internet, but they have friends who do, so they post their houses with help from these friends.
I agree about haggling, and all the houses that are in the website i posted are subject to that when you get to cuba, like any other bussiness.
Greetings
Eric