Add Shipping Cost to "Mark as Shipped"

We use a lot of local carriers for our local customers.  These small local carriers are not in Ship Station, so we use the "Mark as Shipped" function to add the tracking number and push that back to our ERP.  Currently there is no option to add the price for this, so we have to manually go into our ERP and add the shipping cost for all of our local carriers (which adds up to quite a lot of time).