Hirelings:
I'm trying to work out a suitable system to find the cost for hirelings. Due to the generally higher ECL this isn't so simple.
What I'm thinking of is a simple formula based on ECL and special abilities:
Mercenaries
Mercenaries lead a life of fighting. They get more than just age XP, so they are generally younger than the average population at the same ECL. They also have better equipment.
An NPC mercenary can be considered to have at least half his level in the Warrior NPC-class, just to differentiate them from important NPCs and PCs. Their stats are lower than PCs. (NON-elite-array)
As a rule of thumb, and all costs given are per day of hiring:
Mercenaries with at most 2 levels (usually the highest levels) of PC classes:
ECL squared x 1gp for normal fighting mercenaries per day.
Mercenary troupe leaders or Elite mercenaries who have half their levels in PC classes (Fighter, Marshall, Initiator classes, Bards) and Elite Array:
ECL squared x 3gp, and their ECL is expected to be at least 8 for leaders.
Spellcasters who are only Adepts take the same.
Spellcasters who are Adepts with a prestige class (generally SRD-prestige classes) take ECL squared x 3gp
Spellcasters with Elite Array and a prestige class take ECL squared x 3gp
Rogue type characters with many skills with at most two levels of PC-classes:
ECL squared x 1gp
Specialist Rogues with half their levels in PC-classes and Elite Array:
ECL squared x 3gp
Monstrous mercenaries or non-humanoids will use the same rules as the PCs to determine their ECL. Advantageous races will take more money, generally add one gp for a powerful race, and play by common sense.
These prices are for dedicated mercenaries with decent loyalty, and for short-term engagements with at least one highly probable encounter. They will not run at the slightest sign of danger, but won't accept suicide missions, either. All mercenaries withdraw from combat if they have the chance at 30% of their HP, unless it's highly likely that they will win within another round, and they have the initiative. If they have no chance to flee, they will fight for their lives, of course.
You CAN pay less for hirelings (even without haggling them down), but this will increase the chance that they run. You can reduce prices if you arrange them to get a share of loot, and you can also haggle with them. Generally they will want an assessment of the risks involved, and might take less for simple duties like guard duty in a low-risk environment, or more if you go exploring the dungeon of death. Also, if you promise to hire on a long-term basis (at least one month) the price will generally go down, because they will expect a greater amount of paid downtime.
A mercenary troupe will turn you down, initially, if you don't win the Aura check against their leader. In that case you must win with Diplomacy, or offer more money. Play this with common sense and I won't interfere.
Troupes are considered to have one leader type, one healer type, one specialist and one spellcaster per ten grunts. Grunts have a level distribution, and you can expect most mercenaries below ECL 4 to stay back, use ranged combat or use the Aid another action in harder battles. If you hire a troupe and don't want to do all the bookkeeping for a battle, you can just decide that they bind their average ECL x their number worth of CR in enemies, and whittle them down to an appropriate percentage of their HP while you deal with other enemies.
Generally hiring mercenaries will not decrease your XP-award for a battle, since you are paying money for them, and money is at least half of what makes PCs strong. The mercenaries will gain XP as cohorts of their level. (So divide their ECL by your ECL and multiply with the XP you got for the battle.) They are expected to level and will then also ask for more money.
Now for general balancing it much depends on the paperwork you wish to do. With little paperwork you will get smaller gains from hiring mercenaries, and I find nothing wrong with giving greater gains to people who do more paperwork. Generally mercenaries should not be completely optimised, though.
Unless I get serious disagreement with this system, I'll run it like that for now. You can hire yourselves out as mercenaries at rates above those given, if you wish, and you will of course get XP for encounters that play out normally.