It would take a very radical change in the economy of the game to reach a point where cost would factor into the party creation process. I personally doubt this is going to happen.Luckily the game is moddable. I hope there will be some "realism" mods which take into account the very costs to field "nobles". I would opt for about 10% to 15%, that's often the ratio of well armed troops in Dark Age armies.
If we are being realistic. The overwhelming majority of strategic or tactical type games tend to have you favor fielding an elite force, in one way or the other.
Nahh, shields tend to work quite well now. A decently sized and equiped enemy party is going to get to your line, if you just stand there unloading arrows straight to the front...To Khan Guards and Fians, or ranged in general, armor is not the main solution in my opinion. Better blocking with shields is more important, also because most units on the field should be lowly armored normal troops and not plated elites from which there are much too many in the game (I count many T5 into this category too). I often have the feeling that "armor fans" are the no-shield-wreak-havoc-with-twohanders-from-behind guys who need big armor for their unrealistic deeds and who are disturbed by arrows too easily.
Ofcourse, you are just not going to do that.