I have been thinking about this when playing other games, why don't the voodoo require anything but turns?
So here is my suggestion
Voodoo require port materials
So basically now voodoo require port materials to cast, the amount and item requires on the rarity and power of the cast, the ports can be selected in the voodoo menu, and the materials will be taken from that port.
Summoning related voodoo(Call kraken, levi, SoW) require food.
Ship related require Iron and Tools
Port related require rum and/or tobacco
Common cards have a basic cost of 1X. what X is, will be decided based on the card.
Uncommon could be 2X. Meaning that at minimum it will always be twice what a common would cost.
And rare 5X. 5 times what a common would be.
Most of the cards require gold bars to work, Common can be 10, uncommon 20, and rare 50 for example. Certain cards can be specialized-Iron golem for example should not require any supplies but gold bars and turns to cast
Certain cards that include non magical uses(Military service, bribe...etc) require gold coins
Credit for the cost and gold bar goes to Meliva