We use resin moulds as trials and they are formed 500x or more in order to get a stack and test how they sit in transit so a resin mould would be the cheapest way to go. If you are stuck on an aluminium mould like you are saying then yes on a manual machine there is a lot less work involved, and as you say if its only to protect the part then no polishing is needed on the mould just a few vent holes and minimal clean up. It is also possible to get a cast aluminum mould which the price sits between a resin and billet aluminium mould.