Price Tag for hiring a monster as mercenary?

I’m designing a game where players could hire "any" monster as a missionary and fight for him/her.

The only restriction is probably the alignments. After all, a CE monster will NEVER work for a LG character! Or rather, a LG character will never "hire" a CE monster! (All he/she want is kill the xxxx out of him/her/it!). And vice versa.

That’s all good! The only thing I can’t figure out is the "price"!

Apparently it should be based on their CR, but I really can’t figure out the math.

I want the player to hire higher-CR monsters as much opportunity as possible, but I don’t want it to be "too expensive"!

Otherwise the players could just hire whole bunch of low-CR monsters and zerg through everything, what’s the point of hiring any expensive high-CR monsters!?

And if it’s too "cheap", any "challenge" I put forth for them will be "too easy and meaningless"!

I know I could exploit the Leadership feat to put a "cap" on it, but at higher Leadership, the amount of low-level followers are in high double-digits and are in very good fit for the definition "Zerging"!

So I’m really at the end of my rope here, and I can’t find any alternative rules online talking about this. (Most of the things I found is "xxx discount on Amazon"! ~>3<~)

Could somebody PLEASE be so kind and help me out and guide me to the right way!?

Much appreciated!

Baldur’s gate: hire someone as “mercenary”

In Baldur’s Gate 1 and 2 (underlying dnd 2e, forgotten realms), you can add certain members to your party, and remove them freely. When you remove them, they keep the items they wear (which you can strip the moment before), and take no gold with them. I’m trying to roleplay a little, and this is absurd. So, what would be a fair amount of gold to give to a party member for being in a party for some time?

Some thoughts/additional points:

  • I read somewhere that this might be relevant to the amount of battles done. Let it be known that in this case, the amount of battles is maximum: everyday has many dangerous battles.

  • Splitting the party gold is one idea. It still might be unfair if the other characters have used gold to buy more expensive items than the npc leaving.

  • A specific amount of gold per days spent in party would be another idea. I’ve read that this would be dependent on level?

I am hoping that there would actually be some rule about this that I am not aware of.