DES MOINES — Special drug and mental health courts are cost-effective alternatives to prison for offenders battling addictions or other problems, but funding challenges limit the scope and reach within and beyond the 12 communities currently served, members of a new task force were told Thursday.Lettie Prell, director of research for the state Department of Corrections, told the Governor’s Working Group on Justice Policy Reform, drug-court programs cost about $7,400 per participant per year but have proven that every dollar invested in treating offenders who are diverted from prison carries a $9.60 return over a decade.“They’re good investments,” she said, noting that the state spent nearly $3 million to provide services for 657 offenders through the special courts’ program in fiscal 2015.Judge Kirk Daily, who presides over a drug-court program in Ottumwa, said he prefers the alternative sanctions for offenders who need the “intense” services to get sober and “change the way their conduct their lives” to “just warehousing” them in prison, but he told task force members that issues related to declining funding or underfunding has forced providers to donate services to keep the program running and that is not sustainable.“I’m here because I think the program works,” Daily told the initial meeting of a working group Gov.