Hey, Ben.  Are you talking about situations where the bits are freely licensed but a particular distributor is charging you a fee to copy from them as a source?  If so, I try to do what you do above: attach the fee to the verb (the act of copying) not to the thing being copied -- as long as the fee really is imposed only by that source, and is not part of the licensing terms for the bits themselves (because in the latter case, obviously it is not free software and so there is by definition a software freedom non-freeness going on too).  So, assuming the former: "convenience fee for copying", or "trusted-source copying charge", or something like that -- the best phrase will depend on the context in which it's being used.  I think there can't easily be one set phrase that works in all circumstances, precisely because the fee is specific to the verb -- to the particulars of *this* copying situation as opposed to some other way of obtaining the bits -- and not specific to the bits themselves, which would be more or less the same whatever source they're obtained from.

Er, is that useful?