1/2 cargo capcity is a bit too much. 2/3 is livable, but honestly if we skip the custom turrets and make a 100 million dollar license for them that should be more then enough.
So P-Liner as example
9 class 7 turrets (What ever those end up becoming)
4000 cargo
Armour 160 000
Vessel cost of 60 million
License that is also a shield at 150 000, cost of 100 million
Thats 160 million total for that ship. That is more the sufficent in my mind. Of course so is leaving them be, just move them to remote selling planets.