Unit price of a product depending on the quantity of the products of a category

[ilclaudio]

Hi all,
I should add this feature to a Prestashop e-commerce:
The unit price of a product must depend on the quantity of products of a certain category in the cart.

Is it possible with the standard?
Is there a module that accomplishes to this feature or should I modify the Cart module?

Thank you very much for your advices.

cld