Hi,

Currently, the ecommerce module is designed so that product options store relative price difference in currency units.
This value is then used in ProductOptionSelector controls and checkout process controls (in ~\CMSModules\Ecommerce\Controls\ShoppingCart\ folder, mostly ShoppingCartContent.ascx/.cs code)

You would need to calculate the value in your custom code. One question - do you have Kentico CMS Source Code License? It would be helpful, anyway some changes should be possible without it as well.

Do you have experience with Custom E-commerce providers? Please see http://devnet.kentico.com/docs/ecommerceguide/custom_providers_overview.htm

The custom providers will be needed too.

Thank you in advance for your cooperation and response.

Regars,
Zdenek