I would like to make it so, that if a customer buys lets say 10 products, there is an automatic fee of 1€ for each item (10 x 1€ = 10€ in total) added to the cart.
HikaShop has a tax system whereby you can apply a tax to each product with various degrees based on the tax category of the product, location and type of customer, etc. Would that meet your needs ?