disable magento cash on delivery

I want a function to disable cash on delivery payment method from some products in my magento store. The functionality should work something like this: While creating a product, there should be an option to select COD Available or Not Available. If COD Not Available is selected then the customer should not see cash on delivery method in checkout page. And if a user selects multiple products, some having COD Available and Some not then there should be a message in cart that some of the products are not eligible for cash on delivery. My magento store also showing NAN% when we adding tier [login to view URL] want to fix this. My budget is $20 only.