Hi,
You could do it through the shipping fee. If you activate the "shipping price per product" setting of your shipping methods, you can then either enter a flat fee for all the products in the "price per product" setting below in the shipping methods, or, in each product, you can add an extra fee to each shipping method under the "shipping prices" area of the product edit form (that way you can potentially configure different flat fees for different products).
The only drawback is that it would be added to the shipping fee, not the product price.