Join Wilson Goode's prison-mentoring scheme and you could make millions for the American government.
It costs $35,000 (£23,000) year to keep each prisoner behind bars in Philadelphia, where Dr Goode's Amachi charity is based.
He is an ordained minister with over 50 years' service at the First Baptist Church of Paschall in south-west Philadelphia.
The cycle of crime is so destructive that the city spends more on its prisons than it does on its schools.
But Dr Goode's volunteers can make deep inroads into this ruinous cost - by mentoring the children of prisoners.
"I'm here on behalf of your children", he tells inmates at a prison in north Philadelphia, "because if we do nothing, 70% of them will end up in jail themselves."
It is not hard to see how every hour spent with a vulnerable child in Philadelphia translates into significant savings for the state.
But only now have social scientists examined the enormous potential of voluntary groups to contribute to providing services.
A study by the University of Pennsylvania, and an independent research group Partners for Sacred Places, has for the first time placed a cash value on Big Society activities.
The report, published on Saturday, shows the amounts are enormous.
Researchers carried out a long and intensive investigation of the activities of 11 churches and a synagogue in Philadelphia, and calculated a total contribution to the local economy of £50m every year.
There are another 1,000 churches like them in Philadelphia alone, and 300,000 in urban areas across the country.
Marcus Teague's family demonstrates the cost of doing too little.
He has 10 children of his own with five different women, and has been in and out of jail for the last two decades.
One of his sons followed him into crime and was shot dead last September. Now the youngest has been sent to jail, and Marcus Teague is keen for his grandchildren to be mentored.
Following the blueprint
"My son is starting at the same age as I did," he says.
"And my son that was killed... he was following the blueprint that I gave. I don't want his child to grow up the same way as my child did," he adds.
At a high school in a hard-pressed neighbourhood of Philadelphia, mentors win the trust of vulnerable children over games of Scrabble.
One of them, Kezia Lawrence, seems old for her 11 years.
She says children have "a 50-50 chance" of surviving the dangers in their environment.
She lists them dispassionately: "Fighting, shooting, killing, drugs, stuff like that….and you know it's really hard for people to go in the right direction when there are a whole lot of bad influences."
The University of Pennsylvania study looks at what congregations do with unprecedented detail, carrying out exhaustive interviews with clergy and lay members, and inspecting financial records.
The approach revealed social "goods" which are usually overlooked - such as preventing divorce or suicide, or turning a person back from addiction.
Mary Ellen and Michael Desmond are members of one of the churches in the study, St Luke's Episcopal.
They say their marriage would not have survived were it not for the church, and believe that, once parted, they would have been a direct burden on the state.
"If we were to become separated into two households," says Mary Ellen, "in that economic situation, we would have to seek out government help."
Existing research has already put a figure on the economic value of a marriage saved - $18,000 (£12,000).
Averting a suicide is considered to be worth $19,600 (£13,000).
But the researchers have broken new ground by putting a figure on what seem to be even more intangible benefits of voluntary activity.
For example, they valued "teaching pro-social values" to a young child at $375 (£250).
Congregations nurture small businesses, and run kindergartens, soup kitchens, sheltered accommodation and youth groups.
Tuomi Forrest, Vice President of Partners for Sacred Places, insists the research shows that in planning for urban renewal - or a Big Society - religious congregations are cannot be overlooked.
"Funding streams leave them out at the moment, but this study suggests a whole realignment in funding strategies", he says.
"It showed us how little we knew about how congregations impact voluntary activities. Religious organisations need to be taken much more seriously as economic players."
UK churches are also likely to play a critical role if services once the preserve of government are transferred to volunteers.
However, church leaders in Britain have expressed concern that a Big Society might lead to cuts in government spending that hurt the poorest most.
'Not a substitute'
Ram Cnaan, a Professor of Social Policy at the University of Pennsylvania and co-author of the report, agrees that "this magnificent story is not a substitute for public resources".
"In the US, whatever commitment we had to the poor, we have weakened it during the last twenty years", he says. "The government caught up to the activities of congregations and said 'ah-ha, we can let them do it and we can save our money'."
"They said 'here's a willing partner, and one you can contract with and it will cost us less'. It's admirable, but not desirable."
In the basement of St Mary's Episcopal Church, Bike Works is teaching children who might otherwise be on the streets how to build and maintain bikes.
The group aims to broaden their horizons, teach them teamwork and raise their expectations.
So scarce have government services become that the organisation is often side-tracked into providing emergency care - such as finding children food, or somewhere to sleep.
"So many kids are falling through the gaps, and it's the responsibility of society to help them", insists Bike Works' Director, Kitty Heite.
"We aren't social services, and we could do so much more with Bike Works, with the fun thing, if we weren't having to do that.
"Making the voluntary sector responsible for the glue in people's lives is a little scary."
For each of the 600 children who go out later that day to ride in Philadelphia's Fairmont Park, hundreds more are not being reached.
Philadelphia's volunteers question whether a bigger society can be built on smaller spending.