In my current game, I've fought with Verga and he has one city left, a fortress.  Yet he is maintaining a massive army and still making a tiny surplus of gold on 30% taxes.  

I check on his Oppressor unit which is very similar to my Pariden Destiny's Guard unit.  Both have full leather armour, wooden shield and warhammer with three traits. Pariden unit maintenance is 0.9 and Verga's Oppressor maintenance is 0.1.

Verga has the Warlord trait -50% to wages.

Vergas has a full stack of 9 on his city and a second large stack outside.  It' no wonder he can maintain such a vast force from one city with 0.1 unit wages which is nine times less than equivalent troops.

So I can only surmise that this is a big bug in unit costs.  There are no buildings that I can find that would affect the wage costs.  His champion has no traits that seem to affect the price.

Here is the save file: http://www.gamefront.com/files/23601319/P04.rar

Cheers,

Sword