Hello,
If you're talking about that plugin :
www.hikashop.com/marketplace/product/202...rice-by-obsidev.html
There is a mention that you should be aware of :
The "Custom Field price" plugin allows you to configure different fees depending the order custom field values.
That plugin, in its current version, is just working with order custom fields ; not item custom fields.
It would be possible to improve the plugin to also support item custom fields but the algorithm would be a lot different since the current version is adding extra lines in the cart details.
For what I understand of your requirement, you want to add an extra price to the item directly.
Now it could be possible to use the dynamic price system of HikaShop but you would not have the details about the product price and the "options" prices ; just the total of the product with its "options".
While the "custom field price" is just working with order custom fields, there is another plugin which do use item fields :
www.hikashop.com/marketplace/product/146...rice-word-count.html
Regards,