Automatic surcharge based on product / Sales order automatic line inclusion

We quote and sell Fire Extinguishers to customers, and these products are classified as dangerous goods to ship.

It would be good when we quote a customer, or put a sale into the system, that another product/service/freight charge would be automatically added, as it's sometimes forgotten by staff members.

I don't believe that adding the freight cost to the product cost is suitable, as customers often collect from our premises, and doing so will make our product uncompetitive in pricing, likely resulting in lost sales.

This could also be used for products that are above a certain size for example, as couriers would add an oversize/manual handling fee.