Hi,
I think that you will a to make a little plugin.
Create a custom field in the item table, then create a plugin based on the function "onBeforeCartUpdate(&$cartClass,&$cart,$product_id,$quantity,$add,$type,$resetCartWhenUpdate,$force,&$do)" to manage the action when a product is added to the cart, if there is a value in the custom field previously created, get this price, else use the product price.
Here is some documentation about how to create a plugin:
hikashop.com/support/support/documentati...umentation.html#cart
You can use as example this plugin:
www.hikashop.com/forum/2-general-talk-ab...n-plugin.html#118857