Historically, there were very few multi-way shipyards in this time frame. If they implement one it should be your home port only.
As to price premium, the unit price should go down not up to reflect the savings in ordering supplies for more than one build.
I tend to have a L4 shipyard in one of my Indian ports to replace losses without having to send a fleet back home without a profitable cargo (combat fleets). By the time I need one, it's usually very dangerous for a single ship (the replacement) to travel alone.
As to price premium, the unit price should go down not up to reflect the savings in ordering supplies for more than one build.
I tend to have a L4 shipyard in one of my Indian ports to replace losses without having to send a fleet back home without a profitable cargo (combat fleets). By the time I need one, it's usually very dangerous for a single ship (the replacement) to travel alone.