Its probably not a real cost problem, higly advanced worlds will probably have no problem procuring warpships.
But antimatter is another problem entirely if i recall the conversion (as Stated in TNG TM) correctly you need 10 units deuterium to convert into 1 unit antimatter.
Not very cost effective and antimatter can become a very critical commodity if the system in question has no station to convert antimatter in the first place.
Most probalby i still have the traveller System defense tactcs in my head as pointed out in "Imperial Squadrons" and "Pocket Empires".