Later, after the game, I found the section in the original DMG for the price of clerical healing spells.
It's 100 gold for a healing spell.
So, at its simplest, pay 100 gold, get a lay on hands.
However, I wrote this up to provide something a little more detailed. The following rules are meant to provide some additional realism and verisimilitude to the setting. It's little things like this that make the setting feel like a real world.
What the players need to realize is that their characters are not the only people in town who want/need healing, and that there are only so many clerics of level in the temple.
In our campaign, most of the characters worship or pay homage to Justicia, the goddess of justice and mercy.
In Thither, the temple of Justicia is right across the street from a hospital, built by Bo-Mont.
17. Temples to Justicia and Bilgelik. These two new peripteral* temples featuring dozens of gleaming marble columns were built in the last twenty years by wealthy merchant and philanthropist Bo-Mont Oacha.. They are temples to Justicia, Goddess of Justice and Mercy, and Bilgelik, God of Wisdom and Prosperity. The priests and acolytes of these temples endeavor to offer succor for the sick and poor. Their progressive philosophy is very unpopular with the established nobility of the Patricians who occasionally hire mobs of thugs to attack and vandalize the temples and their worshippers.
*peripteral - (of a building) having a single row of pillars on all sides in the style of the temples of ancient Greece.
18. Hospital. Philanthropist Bo-Mont Oacha also constructed this hospital and hired chirurgeons and healing priests of Justicia to tend the wounded gladiators of the arena. The hospital also serves as a school for new healers and chirurgeons.
So, your characters are injured and your own priest is out of healing. You decide go to the hospital (18). You get in line, take a number, and wait in the waiting room for a priest to see you.
The temple of Justicia has one 4th level priest (Bogot), one 3rd level priest (Ota-Ram), two 2nd levels (Zaki, Kibogo), and three 1st levels (Phaisho, Aie-le, Hachugyu). Each priest takes a turn offering prayers of healing for the sick and injured for two hours each day.
Roll a d12 to determine which priest is on duty today.
1. Bogot (4th level)
2. Ota-Ram (3rd level)
3-4. Zaki (2nd level)
5-6. Kibogo (2nd level)
7-8. Phaisho (1st level)
9-10. Aie-Le (1st level)
11-12. Hachugyu (1st level)
Next you roll 1d16 to see where you are in line. You have to wait 10 minutes for each person in front of you. If you roll 12 or higher, you are too late. You'll have to be content with herbs, medicines, poultices, leeches, and chirurgery (+1 Hit Point for the day) and come back tomorrow.
If you get in, the priest makes healing checks for each person in front of you. The priest will continue to pray for each person in line until they receive healing, meaning their Disapproval may increment by the time they get to you. The bad news is that you may not get healing. The good news is that you are only expected to pay a tithe of 100 gold pieces if you actually receive healing. If you do not receive the healing, you are not obligated to offer a tithe.
Absalom is injured and is taken to the temple.
I roll an 11. Hachugyu is on duty today.
Absalom is third in line!
Hachugyu sees to the first person and rolls a 16+1=17. Hachugyu lays on hands for 3 hit dice of healing.
Hachugyu moves to the second person in line. He rolls a 6+1=7. Fail. Disapproval is incremented by 1 to 2.
He tries again: He rolls an 8+1=9. Fail. Disapproval is incremented by 1 to 3.
He tries again: He rolls an 11+1=12. Success! Hachugyu lays on hands for 2 hit dice of healing.
Finally, he comes to Absalom. Chit chats for a bit, asks him where it hurts, etc. He lays his hands on Absalom and offers a prayer to Justicia.
He tries again: He rolls a 3+1=4. DISFAVOR! 3d4 = 5: Hachugyu must undergo the test of humility. For the remainder of that day he must provide foot-rubs, cook dinner, etc. He's also at -10.
He'll try one more time: He rolls a 4+1-10=-5. ANOTHER DISFAVOR! 4d4 = 5 again. His ability to lay on hands is severely debilitated at -20.
Absalom is not going to get any healing today. Hachugyu tried, but apparently Justicia just has it in for Absalom today.