No, you can't work for the highest bidder, because I want players to stick to one thread or the other only, for scouting purposes and such.
As I said, don't worry about the math unless you want to. I'll post charts you can look up.
I'd considered the concept of structuring armies more carefully like that... but it really limits your options. With such a system, you'd not be able to have kobolds vs humans, just to pick an example. You wouldn't be able to have eleven thousand ravens fill the air. Anything that doesn't fill a specific CR would be out. I like a little more variance.
I'm also assuming that since the two sides will have multiple Lords, they'll be playing to their strengths and supporting each other. A single druid, or two for that matter, can't defend an entire kingdom from armies. The druid might be able to crush what he finds, but if he can't find the armies... if, for example, the Light Brigade (posted earlier) split up into squads and scattered across the evil lands, torching towns and spoiling fields... what could two druids do against that? They'd have to be EVERYWHERE at once, and each victory against the light brigade would be a small one... the Light Brigade would be gaining reputation and moral... and little by little evil would be worn down.
On the other hand, if someone on the good team makes up an equivelent level guy, then there're direct counters... both on the defensive and offensive. Variety helps.
It isn't just army vs army... it's army vs land, army vs civillians, army vs politics. All can swing the tide.
Besides... 250,000 gold can buy some nice equipment, tailored to your specific needs. I think that may change the battlefield considerably.