So I've taken a total count of all the flesh heads I want to replace: 96.
The pick-a-brick generic heads; 6-8 variants, all for 25 cents each. Very few of the heads I've seen (that are available in the quantities I need) are cheaper than this. Lego S&H is about $9, which I can afford easily.
A byproduct of my doing this is that I'm going to have a massive surplus of generic flesh heads. The other army I have right now has too small of a pool of generic troops, so my plan is to take the junk flesh heads as a starting point to double the size of their infantry reserves. The only issue is that because they're flesh heads, I want the hands to be Not-Yellow, so that makes pick-a-brick weird. The only torso that doesn't have yellow hands is a fireman torso (there is also a policeman one, but police uniforms are reserved for their opponent's army). What my plan is currently is to just buy torso-leg parts from either pick-a-brick or Bricklink in an installment fashion until I run out of flesh heads. I hope to be done with that project by year's end.