I need some help

I need a second price field(or a text field I don't care) on product variation to appear and be saved on an order.

I added a price field "Supplier price" on the product variation and I need it to appear on the order for data keeping and not change if I change the price on the product variation.

The "Supplier price" value need to be added by the store administrator on the product variation so I can't add this field to the product Line item types.

I almost found the solution

With this simple rules
Event :
After adding a product to the cart

Condition :
Entity has field
Parameter: Entity: [commerce-product], Field: field_prix2

Entity has field
Parameter: Entity: [commerce-line-item], Field: field_prix_fournisseur_line

Action :
Set a data value
Parameter: Data: [commerce-line-item:field..., Value: [commerce-product:field-prix2]

Its working but its not taking the quantity in consideration
I am close!