Format a model attribute

Hi,

I have a problem trying to format an attribute from a model. The model I use is a web service's data model. I have created a simple type "Price" based on the built-in type float (it only adds the symbol "$"). I want to assign this new type to format an attribute from my model (the attribute is a float), but when i try to change the type of the attribute in the context of my component i can't do it because the property "type" is not modifiable.

How can i achieve this?

Thanks in advance.

Pablo