Generally, I have the PC's pay 1,000 GP per level they want to recruit.
It is, aparently, fairly expensive judging by the last numbers. But I'm happy with that.
Thus, a cleric (AKA: Little Floating Orb of Cure) of about 6th level costs 6,000 GP.
I actually have an "adventurer's guild" set up for this kind of thing (I call it Kentucky Fried Questers, but then I have a magic shop in every village called McMagic, so....). They hire out adventurers, serve as a general adventuring-goods store, a place to sell their treasure, and a place to find some evil to slay for quick money, if they need it.
KFQ's policy is that if the guy dies, he's kinda knowing he might in the course of the quest. They make no garuntees, substitutions, or refunds (That 7th level Ranger was defective!

). They do sell insurance policies at higher rates, and often offer to store some extra adventuring booty.
For interesting flavor purposes, every proprietor of KFQ sounds like a civil war vet.
If they want to buy or sell magic items, it's off to the local McMagic's. In fact, for an extra few GP, they can get their already magical weapons super-sized. They can get Extra Value Packs of items that go well together, too.
For interesting flavor purposes, every proprietor of McMagic's is a leprechaun. Odly enough, sine there are no 3e stats for a leprechaun, none have been seen outside of a McMagic's. ^_^
If they want to get some mounts, the local Star Bucks (a stable chain with a particular fetish for riendeer) will hook them up.
For interesting flavor purposes, every proprietor of Star Bucks is a gnome wearing green, and they take off somewhere near Midwinter every year....
If they want a tavern, they can go to Tequilla Bell, where everybody's a stereotype and no one drinks the water.
If the want an inn, it's Sleepway, which bills itself as a healthier, less fattening inn, and recruited some schmuck named Jarod to stand outside and show people his "before" cantrip.
Healing is from the Healing Hut, which is aparently run by a bad imitation of the mafia. And, yes, they do deliver piping hot healing in an hour or less!
Yes, it's silly. But I've had enough of coming up with ideas for new and interesting inns, taverns, adventurers' guilds, magic shops, etc. for every place they go. I just infuse these chains with enough flavor and just enough goofiness to have them make sense. Besides, in a world where prestidigitation can take photos and adventurers can be counted on to save the city (for a price), businesses will spring up to cater to these guys...these famously rich, powerful guys. ^_^
Just wait until I go full-throttle with a McMagic's competitor: Dweomer King.

The PC's will be scamblin' for sure.
Anyhoo, back On-Topic, about hiring adventurers....
I go with a rate of 1,000 GP per level for one lil' adventure. The moment they get out of the dungeon or get out of the forest or grab the dragon's horde, the NPC is gone, off the clock, so to speak. I'm free to say there are no NPC's available in the area (adventuring is dangerous...), and they won't sell and NPC more than 2 levels apart from the PC's level. The NPC is to basically follow orders, much like a cohort, but has no special attatchment to any PC -- his own survival takes prescedence over theirs, if it comes down to it. After all, he doesn't get squat for treasure, just the X,000 GP. Of course, hiring a known theif may have consequenses, and because KFQ provides no insurance about the help they provide, it can lead to some intersting situations.
6th level tag-along: 6,000 GP
Magic Sword: 2,000 GP
Ring of Mind Shieldling: 8,000 GP
Look on party's face when hired hand sneak attacks them and takes their treasure: Priceless
MWAHAHAHAHAHAHAHA!
