Core Fee that is Returnable

I have spent hours looking for something that will work.

What I am trying to do is have specific products require the charging of a "Core Fee" because the item being purchased would be a rebuilt product and we want the customer to return their old part so we can rebuild it.

If they do not return the Old "core" we want to have already charged them for it. If they do return the Old "core" then we wish to refund the customer once we have received the returned "core"

Anyone have any idea how to do this? I've looked at dependent products or required options but they are not really built to handle the return process of just the "core fee".

Maybe I am overlooking something. Any help is appreciated. Thanks.

Anyone?

First time I see someone asking for something like this. But the logic looks straight forward.
In my opinion what you need is refund fee for returned products which can be % from the product's price?
Am I in the right direction?