Well given Humax already have the copy feature on other models I very much doubt there would/is a cost implication or if there is it is negligible.
I've never to my knowledge known of a box have to be replaced because the copy feature wasn't working. No, this is not about cost, it is simply a decision taken by Freesat to not include the feature for reasons unknown.
As said before I am lucky enough to be able to copy from my two Freeview PVRs but the lack of this feature on the Freesat version does make it less attractive in my eyes.