Hello,
I activated the shipping plugin "HikaShop Shipping manual - Prices per product" to activate shipping price per product. But in the product options it's not possible to add a price. Only when I add the product to a warehouse and add the warehouse to a shipping rule the I can add a shipping price to the product. Is this normal behaviour?
Are you talking about the "Shipping prices" tab of your product configuration page ? It should also work if you don't set any warehouse on your product and shipping configuration page.
Can you show me some screenshots of how you configured your shipping method and your product configuration page.