Use galactic market, if every empire could have a positive and balanced economy in all resources the entire idea of a galactic market would become pointless.Economy imbalance:
Most things cost nearly as much alloy, as minerals before, while we have about ¼ of the income, and still require extra buildings for it.
For example, if you are a agressive empire that need a huge fleet you will need buy alloys in market, if you could spam all alloys that you need the idea of galactic market become useless.