Sigil's Lower Ward and the Hive abound with opportunities for characters with a little jink to do some good for folks. Here we'll break down the startup costs and the running operational costs for a few charitable activities in which players can engage. Additional costs, such as bribes for city officials, are not included. These and small social adventures, such as the hunt for a hireling willing to work in a low-class area, or intimidating a local gang into stopping their harassment of the place, are left for the GM to include.
All costs are 3.5e SRD and PFSRD standard and so are easily applicable to other D&D settings, with estimates made for gear not appearing there, especially room costs. (I do not have other sources available to me at the moment.) You are welcome to transplant them.
Even if the players cannot fund these indefinitely, donations to any of these outfits that already exist are certainly suitable charitable contributions for players that would like to make them. The following figures tell you just how much you're supporting by donating 100gp to a soup kitchen or free school; it's also an explanation of at least one thing your money goes to when you donate it to a local church.
Description: This small soup kitchen has a cooking area in the back and a seating area with simple benches and tables for a few dozen people at a time. It is open from mid-antepeak to just after mid-postpeak. It serves about 300 simple meals per day, mostly cheap bread and basic starchy soup, with the occasional vegetable. The drink is usually hot tea made with municipal water. Everyone gets the same meal, but everything is free. Clients are supposedly limited to one meal per day but the staff generally overlook this if someone keeps their head down and doesn't abuse their kindness.
Each day a couple of people who need a little money and have a day to work are hired at untrained rates, 1sp/day, to ladle soup in the line, wash dishes, haul water, etc.
50 sets clay mugs, plates, and spoons: 3gp
Cooking kits (3): 9gp
Flint and steel: 1gp
Long benches and tables: 50gp *
Simple lock: 20gp
Room rental (1 large, w/kitchen/fireplace): 10gp / 30 days
300 Poor meals/day: 5gp/day**
Torches x5, 4hours/day***: 2sp/day
Cook (trained hireling): 3sp/day
2x assistants/servers (untrained hirelings): 2sp/day
* Hard to find good estimates for furniture. Two people sitting on upturned buckets at a barrel are using 3gp worth of furniture!
** 1sp buys a day's worth of Poor meals -- I assume 3 person-meals. This is half that cost: the outfit is not trying to make a profit, and makes a practice of turning remnants and slightly old food into edible meals.
*** Five torches are used for two hours before mid-antepeak and two hours after mid-postpeak.
Total startup: 83gp
Total operational: 190gp / 30 days = 2280gp / year
A Level 11 character who devotes 1% of typical level wealth to starting and running a soup kitchen able to serve 300 meals a day can fund one for 3 months.
A Level 20 character using 1% of wealth to fund such a soup kitchen can fund one for 40 months.
This room hosts a warming stove and a slate board on the back wall. It is furnished with rows of benches and short tables for young students to sit at and practice literacy, ciphering, and basic knowledge of the world. For five days a week, a reasonably educated scribe comes in and spends the day teaching. In the morning, younger students come in and practice basic lettering and arithmetic, livened with occasional lectures on the elements, the planes, types of magic, lists of sentient species, city government, or other basics of Sigilian worldly knowledge. The teacher has a lunch break, and then in the afternoon, older students come in to learn a bit of composition and handwriting along with some classical geometry. They receive more focused lectures on planar history and science. They probably also get a few lectures on philosophy and theology, with an emphasis on the scribe's own faction and religion.
Everything is free. Work is done with slate and chalk; major examinations are oral, in front of the class. Advanced students are permitted a few weeks per year practicing with precious and expensive ink, quill, and parchment.
The room is large enough to handle twenty to thirty students. School meets 5 days a week for 50 weeks of the year, with relatively frequent holidays and a two-week break for the teacher. In Sigil, schools are accredited or at least inspected every now and then by the Bureau of Learning; this school is a legitimate institution on the standard city lists. It is probably named after its funders or funding institution.
Desks and benches: 50gp
Warming stove: 10gp
Slates, x30: 30gp
5'x8' chalkboard installed on wall: 40gp
Simple lock, 20gp
Room rental: 5gp/ 30 days = 60gp/year
Scribe (trained hireling): 3sp/day = 100gp/year
Chalk, 40 pieces/day: 4sp/day * 250 school days = 100gp/year
Repair/replacements: 3sp/ school day = 75gp/year
Parchment, Quills, and Ink: 20gp/year
Total startup: 150gp
Total operational: 356gp / year
A Level 11 character who devotes 1% of typical level wealth to starting and running a free school of this size can start and fund one for the first year, and will hopefully have more income by the time the next year rolls around.
A Level 20 character using 1% of wealth to bankroll such a school can fund one for 20 years.
This small clinic treats serious wounds among the local population. Antitoxin and antiplague are incredibly expensive, and so are just not options for poor clientele. Magical healing is also beyond most of them. Thus, the clinic is staffed by a doctor doing their best with mundane materials and the Heal skill.
The primary purpose of the clinic is to stabilize dying patients. A 1HD commoner who has had any sort of injurious accident or attack is quite likely in negative hitpoints and in need of the most skilled assistance possible in hopes of stabilizing. If it took longer than a few minutes for the patient to arrive, they may have stabilized on their own, but are still at risk of losing hitpoints. As soon as the patient is stable and has had some treatment, another day of long-term care gets them past disabled and to a condition where hit point loss is no longer a concern.
The healer is assumed to be at least an NPC expert, with a +1 bonus to Wis or the Self-Sufficient feat, and 4 ranks in Heal, meaning that under normal circumstances they can take 10 and make the DC 15 checks for first aid and long-term care. Only when treating poison or disease, or under rarer circumstances, is a healer's kit useful.
A healer can provide long-term care to 6 patients at once relatively inexpensively; 2sp per day per person covers sufficient bandages, stitches, soap, herbal salves, and similar medicinal basics per person. If more patients arrive when the clinic is full, emergency service can be provided but the patient must be taken home for long-term care. The doctor's instructions count as a try at aiding another, allowing an untrained friend to attempt a Heal check for long-term care with a possible +2 bonus.
Averaging 5 long-term care patients per day, the clinic can treat perhaps 1500 - 2000 people over the course of a year.
Low beds and blankets x6: 6gp*
Stretchers x4: 4gp
Chair, desk, chest: 5gp
Surgeon's tools: 20gp
Lock, Average: 40gp
* Based on a 5sp blanket and half the cost of the 1gp camp cot for a non-folding version.
Room rental (1 large room, 1 office): 10gp / 30 days, 120gp / year
Doctor, 1gp/day = 360gp/year
Long-term care, averaging 5 patients at a time: 1gp/day = 360gp / year
Common meals for 5 patients: 1.5gp / day = 540gp / year
Midwife's kit, 2/year: 20gp
Total startup costs: 85gp
Total operational costs: 1400 gp/year
A Level 11 character who devotes 1% of typical level wealth to starting and running a free clinic of this size can start and fund one for about 5 or 6 months.
A Level 20 character using 1% of wealth to bankroll such a clinic can start and fund one for about 5 years.
Clinics like this often try to defray operational expenses by having the doctor make healer's kits or alchemical items like antitoxin in their spare time, to sell into Sigil's retail market for warriors and explorers. The amount of spare time available is usually the limiting factor. Clinics that don't provide meals, expecting patients to have family or friends to provide on their own or charging typical inn rates for meal service, are a common sight as well, and save the 540gp/year on meals.
(Meals are full-price because the doctor isn't a chef, and they are Common instead of Poor because the doctor wants his patients eating food with more nutritional value than simple calories! A bit of protein and some greenery is important for a recovering patient.)
There is an interesting variation on the free clinic which involves the planar ally spell. A Level 11 cleric can call a ghaele eladrin and request that they provide healing services to all comers in a poor area; this task is usually quite acceptable to the eladrin. The payment is significant: a level 6 spell, with a level 11 caster, costing 250 XP, and 10,000gp in payment for the 10HP ghaele, totals 11,910gp. However, the ghaele can cast cure light wounds at will, and when preparing for this task will typically prepare many other healing spells such as lesser restoration, remove disease, and remove curse.
The ghaele will remain in Sigil for 11 days. Having been paid for their work already, the eladrin requires no payment from patients for spells that have no material component, and there is often a long line for their services. They will also travel about the area several hours per day, seeking sick people or tending to injuries at accident sites.
The price of the celestial's service is extravagant compared to the cost of running a clinic, but the ghaele can potentially help a very large number of people in a short period of time. Such an event is always accompanied by an outpouring of gratitude and good reputation for the character who finances the blessed visit.
Such creatures almost never come to Sigil on their own to stay for long periods, replacing regular clinics: it's simply not the place of celestials to interfere so blatantly with mortals, and besides, the presence of instant, free healing constantly would harm the development of Sigil's own medical institutions. When a mortal is willing to make the sacrifice to call them, though, they come joyfully.